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GED Science

GED Science Quiz: Apply Chemical Reactions

Practice Apply Chemical Reactions in GED Science with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Apply Chemical Reactions, giving you a quick way to practice the rules, question types, and explanations that matter most for GED Science.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

A student mixes two clear, room-temperature liquids in a beaker. After a few seconds, the student observes that the beaker feels noticeably cold to the touch.

Based on the student's observation, what type of process has occurred?

  1. An exothermic reaction, because energy was released from the mixture into the surroundings.
  2. A precipitation reaction, because a solid must have formed to cause the temperature to drop.
  3. A simple physical change, because the only observable result was a change in temperature.
  4. An endothermic reaction, because energy was absorbed by the mixture from the surroundings.
Explanation: When you encounter a question about temperature changes during chemical or physical processes, you're dealing with energy transfer concepts. The key is understanding whether energy flows into or out of the system. In this scenario, the beaker feels cold after mixing the liquids, which tells you that heat energy moved from the surroundings (including your hand) into the chemical mixture. When a reaction absorbs energy from its surroundings, causing the temperature to drop, this is called an endothermic process. The mixture needed energy to proceed, so it "pulled" heat from everything around it, making the beaker feel cold to touch. Answer D correctly identifies this as an endothermic reaction because energy was absorbed by the mixture from the surroundings, which explains the temperature drop. Answer A is backwards—an exothermic reaction releases energy to the surroundings, making the container feel warm or hot, not cold. Answer B incorrectly assumes that temperature changes must indicate precipitation. While some precipitation reactions do cause temperature changes, the temperature drop alone doesn't prove a solid formed, and precipitation isn't the cause of the energy change. Answer C misses that a chemical reaction likely occurred. Simple physical changes like mixing typically don't cause significant temperature changes unless there's a chemical process happening. Remember this pattern: if a container feels cold during a reaction, think endothermic (energy absorbed). If it feels hot, think exothermic (energy released). The direction of heat flow always tells you about the energy requirements of the process.

Question 2

Which of the following describes a chemical property of a piece of iron?

  1. The iron reacts with oxygen in the air to form rust.
  2. The iron can be hammered into a thin, flat sheet.
  3. The iron is a good conductor of heat and electricity.
  4. The iron is a solid, gray metal at room temperature.
Explanation: When you encounter questions about properties of materials, you need to distinguish between physical and chemical properties. Physical properties describe how something looks, feels, or behaves without changing its chemical identity, while chemical properties describe how a substance reacts or changes into different substances. Option A correctly identifies a chemical property because it describes iron undergoing a chemical reaction. When iron reacts with oxygen to form rust (iron oxide), the iron atoms actually combine with oxygen atoms to create an entirely new substance with different properties than the original iron. This transformation involves breaking and forming chemical bonds. Option B describes malleability, which is a physical property. When you hammer iron into a sheet, you're only changing its shape—the iron remains chemically the same substance. Option C identifies thermal and electrical conductivity, both physical properties that describe how iron behaves without changing its chemical composition. Option D lists appearance and state characteristics (solid, gray, metallic), which are all physical properties describing what iron looks like and how it exists at room temperature. The key distinction is whether the property involves the substance becoming something different chemically. Rusting transforms iron into iron oxide, while hammering, conducting heat, or being gray and solid don't change what iron actually is at the molecular level. For GED Science questions about material properties, always ask yourself: "Does this property involve the substance reacting to become a different chemical?" If yes, it's chemical; if it's just describing appearance or behavior, it's physical.

Question 3

Disposable hand warmers are small packets that produce heat when opened and exposed to air. The packet contains iron powder, which reacts with oxygen from the air in a process that is chemically similar to rusting.

The chemical process that occurs in a hand warmer is an example of what kind of reaction?

  1. An endothermic reaction, because it requires oxygen from the surrounding air to begin.
  2. An exothermic reaction, because it releases a significant amount of energy as heat.
  3. A decomposition reaction, because the iron powder is broken down into simpler elements.
  4. A neutralization reaction, because the heat it produces neutralizes the feeling of cold.
Explanation: When you encounter questions about chemical reactions that produce or absorb heat, you need to classify them based on energy changes. The key clue here is that hand warmers "produce heat" - they release energy to their surroundings. This describes an exothermic reaction, where chemical bonds form and energy is released as heat. The iron powder combines with oxygen from the air (similar to rusting), forming iron oxide and releasing thermal energy that warms your hands. Answer B correctly identifies this as an exothermic reaction because it releases significant energy as heat. Answer A incorrectly calls this endothermic. While the reaction does require oxygen to start, needing a reactant doesn't make a process endothermic. Endothermic reactions absorb heat from surroundings, making them feel cold - the opposite of what happens here. Answer C misidentifies this as decomposition. Decomposition breaks compounds into simpler substances, but here iron powder is combining with oxygen to form a more complex compound (iron oxide). This is actually a synthesis or combination reaction. Answer D confuses the physical sensation with the chemical classification. "Neutralizing cold" isn't a real chemical reaction type. Neutralization specifically refers to acid-base reactions that form salt and water. Remember this pattern: if a chemical process releases heat and warms its surroundings, it's exothermic. If it absorbs heat and cools its surroundings, it's endothermic. The direction of heat flow determines the classification, not what starts the reaction.

Question 4

When a strong acid like hydrochloric acid (HCl) is mixed with a strong base like sodium hydroxide (NaOH), a neutralization reaction occurs. What are the primary products of this type of reaction?

  1. A salt (sodium chloride) and water.
  2. Hydrogen gas and solid sodium metal.
  3. Oxygen gas and a concentrated salt.
  4. A different, weaker acid and a different, weaker base.
Explanation: When you encounter acid-base reactions on the GED, remember that neutralization is one of the most fundamental chemical processes. A neutralization reaction occurs when an acid and base react to form products that are neither acidic nor basic. Let's trace what happens when HCl and NaOH react. The hydrogen ion (H⁺) from the acid combines with the hydroxide ion (OH⁻) from the base to form water (H₂O). Meanwhile, the remaining ions - sodium (Na⁺) from the base and chloride (Cl⁻) from the acid - combine to form sodium chloride (NaCl), which is a salt. The complete reaction is: HCl+NaOH→NaCl+H2O\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O}HCl+NaOH→NaCl+H2​O Choice A correctly identifies both products: a salt (sodium chloride) and water. This is the hallmark of all acid-base neutralization reactions. Choice B describes what might happen in a very different type of reaction involving metals and acids under extreme conditions, not a simple neutralization between HCl and NaOH. Hydrogen gas and solid sodium metal are not products of this reaction. Choice C is incorrect because neutralization reactions don't produce oxygen gas, and the salt formed isn't concentrated - it's simply dissolved in the water that's simultaneously produced. Choice D misunderstands neutralization entirely. The reaction doesn't create weaker acids and bases; instead, it eliminates the acidic and basic properties by forming neutral products. Study tip: Remember the neutralization formula pattern: Acid + Base → Salt + Water. This applies to all strong acid-strong base reactions and is a reliable pattern for GED questions.

Question 5

When the chemical equation H2+O2→H2OH_2 + O_2 \rightarrow H_2OH2​+O2​→H2​O is correctly balanced, what is the coefficient placed in front of H2OH_2OH2​O?

  1. 1
  2. 2
  3. 3
  4. 4
Explanation: When you encounter a chemical equation that needs balancing, you're working with the law of conservation of mass—atoms cannot be created or destroyed in a chemical reaction, so the same number of each type of atom must appear on both sides of the equation. Let's balance H2+O2→H2OH_2 + O_2 \rightarrow H_2OH2​+O2​→H2​O step by step. Start by counting atoms on each side. On the left: 2 hydrogen atoms (from H2H_2H2​) and 2 oxygen atoms (from O2O_2O2​). On the right: 2 hydrogen atoms and 1 oxygen atom (from H2OH_2OH2​O). The hydrogens are already balanced, but we have 2 oxygen atoms on the left and only 1 on the right. To balance the oxygen atoms, we need 2 water molecules on the right side: H2+O2→2H2OH_2 + O_2 \rightarrow 2H_2OH2​+O2​→2H2​O. But now we have 4 hydrogen atoms on the right (2 molecules × 2 H atoms each) and only 2 on the left. We need 2 hydrogen molecules: 2H2+O2→2H2O2H_2 + O_2 \rightarrow 2H_2O2H2​+O2​→2H2​O. Now both sides have 4 hydrogen atoms and 2 oxygen atoms—perfectly balanced! The coefficient in front of H2OH_2OH2​O is 2. Looking at the wrong answers: A) 1 would leave oxygen unbalanced (2 on left, 1 on right). C) 3 would create 6 hydrogen and 3 oxygen atoms on the right, which can't be balanced with whole number coefficients on the left. D) 4 would create 8 hydrogen and 4 oxygen atoms on the right, again impossible to balance. Always start by identifying which atoms are unbalanced, then adjust coefficients to make both sides equal. Work systematically through each element type.

Question 6

A student prepares two saltwater solutions. Solution A is made by dissolving 10 grams of salt in 100 mL of water. Solution B is made by dissolving 25 grams of salt in 100 mL of water. Which statement correctly describes the two solutions?

  1. Solution A is more concentrated than Solution B.
  2. Solution B is more concentrated than Solution A.
  3. Both solutions have the same concentration because the volume of water is the same.
  4. It is impossible to compare concentrations without knowing the water temperature.
Explanation: When you encounter questions about solution concentration, you're being tested on your understanding that concentration measures how much solute (dissolved substance) is present in a given amount of solvent or solution. To compare these solutions, you need to look at the ratio of salt to water in each. Solution A contains 10 grams of salt in 100 mL of water, while Solution B contains 25 grams of salt in the same 100 mL of water. Since Solution B has more than twice the amount of salt dissolved in the same volume of water, it is more concentrated. Think of it like making coffee - more coffee grounds in the same amount of water creates a stronger, more concentrated brew. Looking at the wrong answers: Choice A incorrectly reverses the relationship, claiming that the solution with less salt is more concentrated. Choice C represents a common misconception - while both solutions do use the same volume of water, concentration depends on the amount of solute relative to the solvent, not just the solvent volume alone. The different amounts of dissolved salt create different concentrations despite identical water volumes. Choice D suggests temperature affects our ability to compare concentrations, but temperature isn't needed for this comparison since we're simply looking at the mass-to-volume ratios at a given moment. For GED Science questions about solutions, always focus on the solute-to-solvent ratio. More solute in the same amount of solvent means higher concentration, regardless of other factors that might affect solubility.

Question 7

A wood fire burns more vigorously when air is blown onto it, supplying more oxygen. This demonstrates an increase in reaction rate due to a change in which factor?

  1. The temperature of the wood reactant.
  2. The surface area of the wood reactant.
  3. The concentration of the oxygen reactant.
  4. The presence of a catalyst in the air.
Explanation: When you encounter questions about reaction rates, think about the factors that can speed up or slow down chemical reactions: temperature, concentration, surface area, and catalysts. In this scenario, blowing air onto a fire increases the amount of oxygen available to react with the wood. This directly increases the concentration of oxygen reactant at the reaction site. Higher reactant concentration means more oxygen molecules are available to collide with the wood molecules, leading to more frequent reactions and a more vigorous fire. Answer C is correct because adding more air increases the concentration (amount per unit volume) of oxygen, one of the key reactants in combustion. More oxygen molecules means more opportunities for the chemical reaction to occur. Answer A is incorrect because blowing air doesn't necessarily change the temperature of the wood itself - the wood's temperature might actually decrease slightly from the cooling effect of moving air. Answer B is wrong because the surface area of the wood pieces remains the same when you blow air on them; you're not breaking the wood into smaller pieces. Answer D is incorrect because air doesn't contain catalysts for combustion. Air is simply providing more of the reactant (oxygen) rather than introducing a substance that speeds up the reaction without being consumed. Remember this pattern: when you see questions about factors affecting reaction rates, identify what's actually changing in the scenario. Blowing air = more oxygen = higher concentration of reactant. Don't be fooled by indirect effects or assume catalysts are present without evidence.

Question 8

Instant cold packs, used for treating injuries, typically contain a pouch of water and a separate compartment with a solid chemical like ammonium nitrate. When the inner pouch is broken, the water mixes with the chemical, and the pack becomes very cold.

The process that makes an instant cold pack work is best described as...

  1. an exothermic process, in which the dissolving chemical releases cold into the surroundings.
  2. a combustion reaction, in which the water and the chemical react to consume all nearby heat.
  3. an endothermic process, in which the dissolving of the solid absorbs heat from the surroundings.
  4. a precipitation reaction, in which the formation of a solid requires energy from the pack.
Explanation: When you encounter questions about temperature changes in chemical processes, focus on the direction of heat flow. The key distinction is whether a process absorbs heat from its surroundings (endothermic) or releases heat to its surroundings (exothermic). In an instant cold pack, when ammonium nitrate dissolves in water, the pack becomes cold because the dissolving process requires energy. This energy comes from the thermal energy (heat) already present in the pack and your skin when you hold it. As heat gets absorbed into breaking apart the crystal structure of the solid and forming new interactions with water molecules, the temperature of the pack drops. This is a classic endothermic process, making answer C correct. Answer A is wrong because exothermic processes release heat and would make the pack warm, not cold. Also, chemicals don't "release cold" — cold is simply the absence of heat energy. Answer B incorrectly identifies this as combustion, which involves burning with oxygen and typically produces heat, not absorbing it. Additionally, heat isn't "consumed" — it's transferred. Answer D mischaracterizes what's happening: a solid is dissolving (disappearing), not precipitating (forming), and precipitation reactions don't typically require energy from their container. Remember this pattern: if a chemical process makes something colder, it's endothermic (absorbing heat). If it makes something warmer, it's exothermic (releasing heat). Cold packs absorb heat; hot packs release heat.

Question 9

According to the law of conservation of mass, what must be true for a balanced chemical equation?

  1. The number of molecules on the reactant side must equal the number of molecules on the product side.
  2. The state of matter (solid, liquid, or gas) must be the same for both reactants and products.
  3. The total mass of all the reactants must equal the total mass of all the products.
  4. The reaction must release energy in the form of heat in order to be considered balanced.
Explanation: When you encounter questions about balanced chemical equations, you're dealing with one of chemistry's fundamental principles: the law of conservation of mass. This law states that matter cannot be created or destroyed in a chemical reaction—it can only be rearranged. The correct answer is C because the law of conservation of mass requires that the total mass of all reactants equals the total mass of all products. When you balance a chemical equation, you're ensuring that the same number of each type of atom appears on both sides of the equation. Since mass comes from the atoms themselves, equal numbers of atoms means equal mass. Option A is incorrect because the number of molecules doesn't need to be equal—only the number of each type of atom. For example, in 2H2+O2→2H2O2H_2 + O_2 → 2H_2O2H2​+O2​→2H2​O, there are 3 reactant molecules but only 2 product molecules, yet the equation is perfectly balanced. Option B is wrong because states of matter can change during reactions without violating conservation of mass. Water can freeze or boil, but its mass remains constant regardless of whether it's solid, liquid, or gas. Option D is incorrect because energy release has nothing to do with whether an equation is balanced. Both exothermic (heat-releasing) and endothermic (heat-absorbing) reactions can have balanced equations. Energy changes don't affect the conservation of mass. Remember: balanced equations are about accounting for atoms, not molecules, states, or energy. Count atoms of each element on both sides—they must match.

Question 10

The chemical compound hydrogen peroxide (H2O2H_2O_2H2​O2​) can break down into water (H2OH_2OH2​O) and oxygen gas (O2O_2O2​). The balanced equation is 2H2O2→2H2O+O22H_2O_2 \rightarrow 2H_2O + O_22H2​O2​→2H2​O+O2​. What type of reaction is this?

  1. Synthesis, because two different product substances are formed from one reactant.
  2. Single replacement, because an oxygen atom is displaced from the original molecule.
  3. Combustion, because highly reactive oxygen gas is produced as a product.
  4. Decomposition, because a single compound breaks down into two simpler substances.
Explanation: When you encounter a chemical equation, focus on the pattern: what's happening to the reactants and products? This question tests your ability to classify reaction types based on the relationship between starting materials and end products. Looking at the equation 2H2O2→2H2O+O22H_2O_2 \rightarrow 2H_2O + O_22H2​O2​→2H2​O+O2​, you can see that one compound (hydrogen peroxide) is breaking apart to form two different, simpler substances (water and oxygen gas). This is the defining characteristic of a decomposition reaction - a single compound splits into multiple products. The correct answer is D. Let's examine why the other options don't fit. Choice A describes synthesis incorrectly - while two products are formed, synthesis reactions combine simpler substances into more complex ones, which is the opposite of what's happening here. Choice B misidentifies this as single replacement, but single replacement involves one element replacing another in a compound (like A+BC→AC+BA + BC \rightarrow AC + BA+BC→AC+B), not a compound breaking apart entirely. Choice C confuses the presence of oxygen gas with combustion, but combustion specifically requires a fuel reacting with oxygen to produce energy, carbon dioxide, and water - not simply the production of oxygen as a product. For the GED Science exam, remember this pattern: decomposition reactions always follow the format "one reactant → multiple products." If you see a single compound on the left side of the arrow and multiple simpler substances on the right, you're looking at decomposition. This pattern recognition will serve you well on similar questions.

Question 11

Which of the following properties is characteristic of a basic (alkaline) solution?

  1. It has a distinctly sour taste and reacts with many metals to produce hydrogen gas.
  2. It has a pH value that is less than 7 and is a good conductor of electricity.
  3. It feels slippery to the touch and causes red litmus paper indicator to turn blue.
  4. It is typically non-reactive and has a pH that is exactly 7.
Explanation: When you encounter questions about acids and bases, focus on the key properties that distinguish these solution types. Understanding pH scale relationships and characteristic behaviors will help you identify the correct solution type. Basic (alkaline) solutions have several distinctive properties. They feel slippery or soapy to the touch because they react with oils in your skin to form soap-like compounds. They also turn red litmus paper blue, which is a classic indicator test. These solutions have pH values greater than 7, with higher numbers indicating stronger bases. Answer C correctly identifies two key characteristics of basic solutions: the slippery feel and the ability to turn red litmus paper blue. Both properties are reliable indicators you can use to identify alkaline solutions. Answer A describes acidic solutions, not basic ones. Acids have sour tastes and react with metals to produce hydrogen gas - this is completely opposite to what the question asks for. Answer B also describes acidic properties, specifically mentioning pH less than 7, which defines acids rather than bases. While bases are also good electrical conductors due to their ions, the pH description makes this answer incorrect. Answer D describes neutral solutions with pH exactly 7, like pure water, not basic solutions. For GED Science, remember that acids and bases have opposite properties. Create a simple comparison chart: acids are sour, turn blue litmus red, and have pH below 7, while bases are slippery, turn red litmus blue, and have pH above 7. This pattern appears frequently on the exam.

Question 12

An enzyme in saliva called amylase helps to rapidly break down starches into sugars as you chew. Amylase is a biological catalyst. How does amylase speed up this chemical reaction?

  1. It provides an alternative reaction pathway that has a lower activation energy.
  2. It increases the local temperature of the starch to make it react faster.
  3. It increases the concentration of starch molecules in the immediate area.
  4. It is consumed during the reaction, releasing energy that fuels the breakdown.
Explanation: When you encounter questions about enzymes and catalysts, focus on their fundamental mechanism: they speed up reactions by lowering the energy barrier that reactants must overcome. Enzymes like amylase work by providing an alternative reaction pathway with lower activation energy. Think of activation energy as a hill that molecules must climb to react. Enzymes create a tunnel through that hill, making it easier for starch molecules to break apart into sugars. The enzyme temporarily binds to the starch, forming an enzyme-substrate complex that makes bond breaking more favorable, then releases the products unchanged. Choice A correctly describes this mechanism - enzymes lower activation energy by offering an alternative pathway. Choice B is incorrect because enzymes don't generate heat to speed reactions. While higher temperatures can increase reaction rates, that's not how enzymes function. Choice C misrepresents enzyme action. Enzymes don't concentrate reactants; they work at the molecular level by binding to individual substrate molecules and facilitating their transformation. Choice D contains a critical error about enzyme behavior. True catalysts, including enzymes, are never consumed during reactions. Amylase emerges from each reaction cycle unchanged and ready to catalyze another starch molecule. If enzymes were consumed, your body would need to constantly replace them, making digestion extremely inefficient. Remember this key principle for the GED: all catalysts (biological or chemical) work by lowering activation energy, not by being consumed or changing reaction conditions like temperature or concentration.

Question 13

A student observes several changes in a lab. Which of the following observations describes a chemical change?

  1. A block of ice melts into a puddle of water.
  2. A spoonful of sugar dissolves completely in a cup of hot tea.
  3. A silver spoon becomes tarnished and darkens over time.
  4. Liquid water turns into steam when it is boiled on a stove.
Explanation: When you encounter questions about physical versus chemical changes, focus on whether the substance's molecular composition has changed. Physical changes alter appearance or state but keep the same molecules, while chemical changes create entirely new substances with different molecular structures. The correct answer is C because tarnishing involves a chemical reaction. When silver reacts with sulfur compounds in the air, it forms silver sulfide, a completely different compound with new properties. The silver atoms have bonded with sulfur atoms, creating new molecules that didn't exist before. This chemical change is irreversible through simple physical means. Let's examine why the other options are wrong. Option A describes melting ice, which is purely physical—the H₂O molecules remain unchanged, just moving from a solid arrangement to a liquid one. Option B involves dissolving sugar, another physical change where sugar molecules separate and mix with water molecules, but no new compounds form. The sugar could be recovered by evaporating the water. Option D shows water boiling into steam, which is simply a phase change from liquid to gas—still the same H₂O molecules. For GED Science success, remember this key distinction: if you can reverse the change through simple heating, cooling, or separation techniques, it's likely physical. If the change requires breaking and forming chemical bonds to reverse (or can't be reversed at all), it's chemical. Look for clues like color changes that aren't just mixing, gas production, heat/light emission, or formation of precipitates.

Question 14

A solution is tested and found to have a pH of 3. How would this solution be best described?

  1. Strongly basic, because a low number on the pH scale indicates high alkalinity.
  2. Strongly acidic, because its pH value is significantly below the neutral value of 7.
  3. Effectively neutral, because it is much closer to 0 than it is to 14 on the pH scale.
  4. Weakly acidic, because it is only a few numerical units away from the neutral point.
Explanation: When you encounter pH questions on the GED, remember that the pH scale measures how acidic or basic a solution is, with 7 as the neutral point. Values below 7 are acidic, and values above 7 are basic. A solution with pH 3 is strongly acidic because it's significantly below the neutral value of 7. The pH scale is logarithmic, meaning each unit represents a 10-fold change in acidity. A pH of 3 is actually 10,000 times more acidic than neutral water (pH 7), making it quite strong. This confirms answer B is correct. Let's examine why the other choices are wrong: Choice A incorrectly states that low pH numbers indicate high alkalinity. This is backwards - low pH values (0-6) indicate acidity, while high pH values (8-14) indicate alkalinity or basicity. Choice C suggests the solution is neutral because 3 is closer to 0 than to 14 mathematically. However, neutrality on the pH scale is defined specifically as pH 7, regardless of where a value falls numerically between the scale's endpoints. Choice D calls pH 3 "weakly acidic" because it's only four units from neutral. This ignores the logarithmic nature of the pH scale. Being four units away from neutral actually represents an extremely significant difference in acidity. For GED success, memorize this key relationship: pH below 7 = acidic, pH of 7 = neutral, pH above 7 = basic. The further from 7, the stronger the acid or base.

Question 15

Lemon juice has a pH of approximately 2, while black coffee has a pH of approximately 5. Which statement correctly compares the two substances?

  1. Both lemon juice and coffee are basic because their pH values are low.
  2. Lemon juice is more acidic than black coffee.
  3. Black coffee is more acidic than lemon juice.
  4. Lemon juice is weakly acidic, while black coffee is neutral.
Explanation: When you encounter pH questions on the GED Science exam, remember that pH is a logarithmic scale measuring how acidic or basic a substance is. The scale runs from 0 to 14, where 7 is neutral, values below 7 are acidic, and values above 7 are basic (alkaline). Lower pH numbers mean higher acidity. Since lemon juice has a pH of 2 and black coffee has a pH of 5, both substances are acidic because their pH values are below 7. However, lemon juice is significantly more acidic than black coffee because it has the lower pH value. The logarithmic nature of the pH scale means that each unit represents a 10-fold difference in acidity, so lemon juice is actually about 1,000 times more acidic than black coffee. Looking at the wrong answers: Choice A incorrectly states that both substances are basic because of their low pH values – this is backwards, as low pH values indicate acidity, not basicity. Choice C reverses the relationship, claiming black coffee is more acidic than lemon juice, when the opposite is true since 2 is lower than 5 on the pH scale. Choice D incorrectly categorizes black coffee as neutral when its pH of 5 clearly falls in the acidic range. For pH questions, remember this key pattern: lower numbers = more acidic, higher numbers = more basic. Also, memorize that 7 is neutral – anything below is acidic, anything above is basic. This fundamental concept appears frequently on the GED Science exam.

Question 16

A chemist adds salt to a beaker of water at 25°C and stirs. After a certain point, no more salt will dissolve, and any additional salt added settles at the bottom. What term best describes the solution at this point?

  1. Unsaturated, because more salt could be dissolved if the solution were heated.
  2. Supersaturated, because it contains more dissolved salt than it can normally hold.
  3. Dilute, because the salt that has settled at the bottom is no longer part of the solution.
  4. Saturated, because it has dissolved the maximum amount of salt possible at that temperature.
Explanation: This question tests your understanding of solution chemistry, specifically the concept of solubility limits. When you see a scenario where no more solute will dissolve despite continued stirring, you're dealing with a fundamental solubility principle. The correct answer is D because a saturated solution is defined as one that contains the maximum amount of solute that can be dissolved in a given amount of solvent at a specific temperature. Once the solution reaches this point, any additional salt simply settles at the bottom as undissolved solid. This is exactly what's happening in the beaker. Let's examine why the other choices are incorrect. Choice A incorrectly identifies this as unsaturated. While it's true that heating could dissolve more salt, the question asks about the current state at 25°C. An unsaturated solution would still be able to dissolve more solute at the given temperature. Choice B confuses this with supersaturated, which occurs when a solution contains more dissolved solute than it normally could at that temperature—typically achieved by cooling a hot, saturated solution. Choice C misunderstands what "dilute" means. Dilute refers to a solution with a low concentration of solute, not whether undissolved material is present. Remember this pattern for the GED: when you see undissolved solute settling at the bottom despite stirring, and the temperature is constant, you're looking at a saturated solution. The key indicator is that equilibrium has been reached between dissolved and undissolved solute.

Question 17

A student wants to dissolve the maximum possible amount of sugar in a cup of water. Which of the following actions would most effectively increase the solubility of sugar in water?

  1. Placing the cup of water in a refrigerator to cool it down.
  2. Using a single large sugar cube instead of granulated sugar.
  3. Heating the water before adding the sugar to it.
  4. Adding a small amount of vegetable oil to the water.
Explanation: When you encounter solubility questions, remember that solubility describes how much solute (like sugar) can dissolve in a solvent (like water) under specific conditions. The key factors affecting solubility are temperature, particle size, and the chemical nature of both substances. Heating the water before adding sugar (C) is the most effective approach because temperature has the greatest impact on sugar's solubility in water. As temperature increases, water molecules move faster and can interact more effectively with sugar molecules, breaking them apart and allowing significantly more sugar to dissolve. This is why hot tea can hold much more sugar than iced tea. Let's examine why the other options won't maximize solubility: Option A is counterproductive—cooling water in a refrigerator decreases molecular motion, reducing the water's ability to dissolve sugar. Cold water holds much less dissolved sugar than warm water. Option B confuses surface area with solubility. While using granulated sugar instead of a large cube would help sugar dissolve faster (due to increased surface area), it doesn't change the maximum amount that can dissolve. The question asks about solubility, not dissolution rate. Option D introduces a fundamental chemistry error. Vegetable oil is nonpolar and doesn't mix with water (polar), so adding oil would actually interfere with the dissolution process rather than help it. For GED science questions about solubility, remember this pattern: temperature is usually the most powerful factor for increasing how much solid can dissolve in a liquid, especially for substances like sugar in water.

Question 18

A scientist tests an unknown clear liquid. The liquid reacts with a strip of zinc metal to produce bubbles of hydrogen gas, and it turns blue litmus paper red. Based on these results, the unknown liquid is most likely which of the following?

  1. A strong base
  2. Pure water
  3. An acid
  4. A saturated salt solution
Explanation: When you encounter a question about identifying unknown substances, focus on the chemical properties and reactions described. Two key tests can help you identify whether a substance is acidic, basic, or neutral: litmus paper tests and reactions with metals. The unknown liquid shows two telltale signs of an acid. First, it turns blue litmus paper red, which is the classic test for acids - acids always turn blue litmus red, while bases turn red litmus blue. Second, the liquid reacts with zinc metal to produce hydrogen gas bubbles. This is a characteristic reaction of acids with certain metals, where the acid donates hydrogen ions (H⁺) that combine to form hydrogen gas. Looking at the wrong answers: Choice A (strong base) is incorrect because bases turn blue litmus paper blue, not red, and don't typically react with zinc to produce hydrogen gas. Choice B (pure water) is wrong because water is neutral - it wouldn't change litmus paper color and doesn't react with zinc under normal conditions. Choice D (saturated salt solution) is incorrect because most salt solutions are neutral and wouldn't turn litmus paper red or react with zinc to produce hydrogen gas. The correct answer is C - the substance is an acid. For GED Science success, remember that litmus paper color changes are your most reliable indicator of pH: blue litmus turns red in acid, red litmus turns blue in base. Also, memorize that acids commonly react with metals to produce hydrogen gas - this reaction pattern appears frequently on chemistry questions.

Question 19

The burning of propane gas (C3H8C_3H_8C3​H8​) in a barbecue grill is a common example of a combustion reaction. What are the typical products of the complete combustion of a hydrocarbon like propane?

  1. Carbon dioxide and water
  2. Carbon monoxide and water
  3. Soot (solid carbon) and hydrogen gas
  4. Oxygen and a different hydrocarbon
Explanation: When you encounter combustion questions on the GED Science exam, focus on what "complete combustion" means. Complete combustion occurs when there's sufficient oxygen present, allowing hydrocarbons to burn entirely and produce the most oxidized forms of their constituent elements. For any hydrocarbon (a compound containing only carbon and hydrogen), complete combustion follows a predictable pattern. The carbon atoms combine with oxygen to form carbon dioxide (CO2CO_2CO2​), while the hydrogen atoms combine with oxygen to form water (H2OH_2OH2​O). For propane, the balanced equation is: C3H8+5O2→3CO2+4H2OC_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2OC3​H8​+5O2​→3CO2​+4H2​O This confirms that answer A (carbon dioxide and water) is correct. Answer B (carbon monoxide and water) represents incomplete combustion, which occurs when there's insufficient oxygen. Carbon monoxide forms instead of carbon dioxide because there isn't enough oxygen to fully oxidize all the carbon atoms. Answer C (soot and hydrogen gas) also describes incomplete combustion products. When oxygen is severely limited, solid carbon (soot) can form, and some hydrogen may remain unreacted as gas rather than forming water. Answer D (oxygen and a different hydrocarbon) is chemically impossible. Combustion consumes oxygen as a reactant; it doesn't produce oxygen. Additionally, combustion breaks down the original hydrocarbon rather than creating new ones. Remember this pattern: complete combustion of any hydrocarbon always produces carbon dioxide and water. The word "complete" is your key—it tells you there's enough oxygen for full oxidation of both carbon and hydrogen.

Question 20

Which of the following is the strongest evidence that a chemical reaction has occurred?

  1. A solid substance melts into a liquid when it is gently heated.
  2. Two clear solutions are mixed, and a cloudy, solid substance forms.
  3. A puddle of water on the sidewalk evaporates on a sunny day.
  4. A colored powder disappears completely when stirred into a glass of water.
Explanation: When you encounter questions about chemical versus physical changes, focus on whether new substances with different properties are being formed. Chemical reactions create entirely new materials, while physical changes only alter the form or state of existing substances. Option B represents the strongest evidence of a chemical reaction because when two clear solutions mix and produce a cloudy solid (called a precipitate), new chemical bonds are forming to create a completely different substance. This precipitate has different properties than either of the original clear solutions and cannot be easily separated back into its original components. Let's examine why the other options represent physical changes, not chemical reactions. Option A describes melting, which is simply a phase change from solid to liquid - the substance remains chemically identical, just in a different state. Option C shows evaporation, another phase change where liquid water becomes water vapor without any change in chemical composition. Option D describes dissolving, where the colored powder disperses throughout the water but remains the same substance at the molecular level; it could be recovered by evaporating the water. The key difference is that physical changes are typically reversible and don't create new substances, while chemical reactions produce new materials with different properties. Formation of a precipitate, gas bubbles, color changes (that aren't just mixing), temperature changes without external heating/cooling, and production of light are all strong indicators of chemical reactions. For GED Science success, remember this rule: if you can easily reverse the process and get back exactly what you started with, it's likely a physical change.