- A laboratory solution has a hydroxide ion concentration of 2.0×10−4 M at 25°C. A student needs to determine if this solution can neutralize 50 mL of 1.0×10−3 M HCl. What volume of the hydroxide solution is required for complete neutralization?
Answer: 250 mL of the hydroxide solution is needed because the acid has five times higher concentration requiring proportional volume adjustment
For neutralization: moles of H+ = moles of OH-. HCl provides (50 mL)(1.0 × 10−3 M) = 5.0 × 10−5 moles H+. The base provides (V mL)(2.0 × 10−4 M) OH-. Setting equal: 5.0 × 10−5 = V × 2.0 × 10−4, so V = 250 mL. Choice A incorrectly calculates the concentration ratio. Choice B uses wrong concentration ratio. Choice D incorrectly assumes volume equality regardless of concentration. - The human body maintains the pH of blood within a very narrow range of 7.35 to 7.45. A condition called alkalosis occurs if the blood pH rises above 7.45. Which of the following would be consistent with a state of alkalosis?
Answer: A decrease in the concentration of hydrogen ions [H+].
When you encounter pH questions on the HESI, remember that pH and hydrogen ion concentration have an inverse relationship. Understanding this fundamental concept is crucial for analyzing acid-base balance in the body.
Alkalosis occurs when blood pH rises above 7.45, making the blood more basic (less acidic). Since pH is defined as the negative logarithm of hydrogen ion concentration (pH=−log[H+]), when pH increases, the concentration of hydrogen ions must decrease. This inverse relationship means that fewer H⁺ ions are present in alkalotic blood, which is exactly what answer choice B describes.
Let's examine why the other options are incorrect. Choice A suggests an increase in H⁺ concentration, which would actually lower the pH and cause acidosis, not alkalosis. Choice C describes a neutral solution where [H⁺] equals [OH⁻], which occurs at pH 7.0 - this is neither acidosis nor alkalosis, but normal neutrality. Choice D indicates increased carbonic acid concentration, which would release more H⁺ ions into the blood, lowering pH and causing acidosis rather than alkalosis.
For HESI success, always remember the pH-hydrogen ion inverse relationship: high pH means low H⁺ (alkalosis), and low pH means high H⁺ (acidosis). When you see acid-base questions, immediately think about whether the condition described would increase or decrease hydrogen ions, then work backwards to determine the pH effect. - A buffer solution is prepared to resist changes in pH. Which combination of substances is most suitable for creating an effective buffer?
Answer: A weak acid and its conjugate base
When you encounter buffer questions, focus on the fundamental principle: buffers work by having a system that can neutralize both added acids and bases through equilibrium shifts.
A buffer requires a weak acid and its conjugate base working together. The weak acid can donate protons (H⁺) when a base is added, while the conjugate base can accept protons when an acid is added. This dual capability maintains relatively stable pH because the system shifts equilibrium rather than allowing dramatic pH changes.
Choice B correctly identifies this essential pairing. The weak acid partially dissociates in solution, establishing an equilibrium with its conjugate base. When you add acid or base to this system, Le Châtelier's principle drives the equilibrium to counteract the change.
Choice A fails because strong acids and strong bases completely dissociate, leaving no equilibrium system to shift. They would simply neutralize each other completely rather than creating a buffering capacity.
Choice C is incorrect because strong acids completely dissociate, meaning there's no meaningful equilibrium between the acid and its conjugate base. The conjugate base of a strong acid is extremely weak and provides no buffering capacity.
Choice D doesn't work because weak acids and weak bases don't form the conjugate pair relationship necessary for effective buffering. Without this specific relationship, the system lacks the coordinated response needed to resist pH changes.
Remember this pattern: effective buffers always involve conjugate acid-base pairs where the acid component is weak. Look for "weak acid + conjugate base" combinations in buffer questions.
- According to the Arrhenius definition, what defines a substance as a base?
Answer: It produces hydroxide ions (OH-) when dissolved in water.
When you encounter questions about acid-base definitions, you need to distinguish between the three major theories: Arrhenius, Brønsted-Lowry, and Lewis. Each defines acids and bases differently, so identifying which theory the question asks about is crucial.
The Arrhenius definition is the most straightforward and focuses specifically on what happens when substances dissolve in water. According to Svante Arrhenius, a base is any substance that produces hydroxide ions (OH⁻) when dissolved in water. For example, when sodium hydroxide (NaOH) dissolves in water, it releases OH⁻ ions, making it an Arrhenius base. This makes option C correct.
Let's examine why the other choices are wrong. Option A describes the Brønsted-Lowry definition of a base (proton acceptor), not the Arrhenius definition. Option B describes a Brønsted-Lowry acid (proton donor), which is the opposite of what we're looking for. Option D describes an Arrhenius acid, which increases H⁺ concentration in water—again, the opposite of a base.
The key distinction is that Arrhenius theory is water-specific and ion-focused, while Brønsted-Lowry theory is about proton transfer and works in any solvent. Remember this pattern: on the HESI, acid-base questions often test whether you can match the correct definition to the correct theory. Always read carefully to see which scientist or theory is mentioned, as this determines which definition applies.
- A patient is experiencing metabolic acidosis, a condition where the blood pH drops. The bicarbonate buffer system in the blood works to counteract this change. Which of the following describes the primary action of the bicarbonate buffer in this situation?
Answer: The bicarbonate ion (HCO3-) acts as a weak base to accept excess H+ ions.
When you encounter acid-base balance questions on the HESI, focus on understanding how buffer systems maintain pH homeostasis. The bicarbonate buffer system is the body's most important extracellular buffer, consisting of carbonic acid (H₂CO₃) and bicarbonate ion (HCO₃⁻).
In metabolic acidosis, excess hydrogen ions (H⁺) flood the bloodstream, dropping the pH below normal. The bicarbonate buffer system responds by having the bicarbonate ion (HCO₃⁻) act as a weak base, accepting these excess H⁺ ions to form carbonic acid (H₂CO₃). This reaction removes free hydrogen ions from solution, preventing the pH from dropping further.
Choice A is backwards—in acidosis, you need to remove H⁺ ions, not add more. Carbonic acid would worsen the situation by releasing additional hydrogen ions. Choice C represents a common misconception; buffer systems resist pH changes but don't completely neutralize acids—they work within limits and maintain equilibrium. Choice D incorrectly describes the mechanism; bicarbonate doesn't release hydroxide ions directly. Instead, it accepts hydrogen ions, which indirectly helps stabilize pH.
The correct answer is B because the bicarbonate ion functions as the base component of this buffer pair, accepting excess H⁺ ions during acidotic conditions.
For HESI success, remember that buffer systems always work in pairs: one component handles excess acid (base accepts H⁺), while the other handles excess base (acid donates H⁺). Focus on which component is needed based on the pH disturbance direction.
- A chemistry student is asked to identify an unknown solution. The solution tastes sour and reacts with zinc metal to produce hydrogen gas. These characteristics are typical of what kind of substance?
Answer: An acid
When you encounter questions about identifying chemical substances based on their properties, focus on the characteristic behaviors that distinguish acids, bases, and other compounds.
The two key properties described here—sour taste and reaction with zinc to produce hydrogen gas—are classic identifying characteristics of acids. Acids have a distinctive sour taste (think lemon juice or vinegar) and react with metals like zinc according to the reaction: Zn+2H+→Zn2++H2. The hydrogen ions (H⁺) from the acid are what drive this gas-producing reaction.
Looking at the wrong answers: (B) A base would taste bitter, not sour, and wouldn't produce hydrogen gas when mixed with zinc. Bases contain hydroxide ions (OH⁻) or accept protons, giving them completely different chemical behavior. (C) A pure solvent like water has a neutral pH around 7, tastes neither sour nor bitter, and doesn't react with zinc under normal conditions to produce gas. (D) An ionic salt might dissolve in water but typically doesn't taste sour or react with metals to generate hydrogen gas—salts are usually the products of acid-base reactions, not reactants with metals.
For HESI chemistry questions, memorize these acid identifiers: sour taste, pH below 7, reaction with metals producing hydrogen gas, and ability to neutralize bases. These property-based identification questions are common, so practice connecting observable characteristics to substance types rather than just memorizing formulas. - Solution X has a pH of 9, and Solution Y has a pH of 12. Which statement correctly compares the two solutions?
Answer: Solution Y is 1,000 times more basic than Solution X.
When you encounter pH comparison questions, remember that the pH scale is logarithmic, meaning each unit represents a 10-fold change in hydrogen ion concentration. This logarithmic relationship is crucial for calculating the actual differences between solutions.
To compare these solutions, you need to calculate the difference in hydrogen ion concentration. Solution X (pH 9) has a hydrogen ion concentration of 10−9 M, while Solution Y (pH 12) has 10−12 M. Since basicity is inversely related to hydrogen ion concentration, Solution Y is 10−1210−9=103=1,000 times more basic than Solution X.
Option A incorrectly suggests a simple arithmetic relationship (12 - 9 = 3), but pH doesn't work this way. The 3-unit difference represents a logarithmic change, not a linear one. Option B makes two errors: it focuses on acidity rather than basicity, and while the 1,000-fold difference is numerically correct, it's backwards—Solution X is actually 1,000 times more acidic than Solution Y, not the other way around. Option D falls into the same trap as A, treating the pH scale as if it were linear (3 × 10 = 30).
For HESI success, always remember that pH questions test your understanding of logarithmic scales. When calculating differences between pH values, convert to the actual ion concentrations using powers of 10, then compare. Each pH unit represents a 10-fold change, so a 3-unit difference means 103=1,000 times difference in concentration. - A student preparing buffer solutions needs to understand the relationship between pH and pOH. If a solution at 25°C has a pOH of 3.7, and the student dilutes this solution with pure water until the volume doubles, what will be the approximate new pH?
Answer: The new pH will be approximately 10.0 because dilution decreases hydroxide concentration by half, changing pOH to 4.0
Initial pOH = 3.7, so initial pH = 14.0 - 3.7 = 10.3. When diluted by factor of 2, [OH-] decreases by factor of 2, so pOH increases by log(2) = 0.3 to become 4.0. New pH = 14.0 - 4.0 = 10.0. Choice B incorrectly calculates the final pH. Choice C incorrectly assumes pH increases with dilution of a base. Choice D uses impossible pH values above 14.
- Which statement best explains why a 1 M solution of hydrochloric acid (HCl) has a much lower pH than a 1 M solution of acetic acid (CH3COOH)?
Answer: HCl dissociates completely in water, releasing more H+ ions than the partially dissociating acetic acid.
When you encounter pH comparison questions, focus on the fundamental concept of acid strength, which determines how completely an acid releases hydrogen ions in solution.
The key difference between HCl and acetic acid lies in their dissociation behavior. HCl is a strong acid that dissociates completely in water: HCl→H++Cl−. This means every HCl molecule releases one H⁺ ion. In contrast, acetic acid is a weak acid that only partially dissociates: CH3COOH⇌H++CH3COO−. Most acetic acid molecules remain intact, releasing far fewer H⁺ ions. Since pH directly reflects H⁺ concentration, the completely dissociating HCl produces a much lower pH than the partially dissociating acetic acid, even at identical molar concentrations.
Option A is incorrect because both solutions have the same concentration (1 M). Option B misses the point entirely—while acetic acid does have more hydrogen atoms per molecule, only one is acidic and releasable. The total number of hydrogen atoms doesn't determine acidity. Option D presents a false generalization. Many organic acids exist, and molecular origin (organic vs. inorganic) doesn't determine acid strength. Option C correctly identifies that complete dissociation versus partial dissociation explains the pH difference.
Remember this pattern: when comparing acids of equal concentration, strong acids (complete dissociation) always produce lower pH values than weak acids (partial dissociation). The degree of ionization, not concentration or molecular structure, determines the pH difference. - Normal rainwater is slightly acidic with a pH of about 5.6. Acid rain, however, can have a pH of 4.6. This one-unit drop in pH indicates that acid rain is...
Answer: 10 times more acidic than normal rainwater.
When you encounter pH questions, remember that the pH scale is logarithmic, meaning each unit represents a 10-fold change in acidity. This is crucial for interpreting seemingly small numerical differences.
To solve this problem, you need to calculate the difference in hydrogen ion concentration between the two pH values. The formula is: [H+]=10−pH
For normal rainwater (pH 5.6): [H+]=10−5.6
For acid rain (pH 4.6): [H+]=10−4.6
To find how many times more acidic acid rain is, divide the acid rain concentration by normal rainwater concentration:
10−5.610−4.6=10−4.6−(−5.6)=101.0=10
This confirms that answer A is correct—acid rain is 10 times more acidic than normal rainwater.
Answer B (1 time more acidic) incorrectly treats the pH scale as linear rather than logarithmic. Answer C (slightly less acidic) reverses the relationship entirely—a lower pH means higher acidity, not lower. Answer D (10 times less acidic) gets the magnitude right but the direction wrong, suggesting the student calculated correctly but misinterpreted which solution was more acidic.
Remember this key principle: on the logarithmic pH scale, each whole number decrease represents a 10-fold increase in acidity. This pattern appears frequently in science sections, so practice converting between pH units and actual hydrogen ion concentrations. - In the reversible reaction NH3+H2O⇌NH4++OH−, how is water (H2O) functioning according to the Brønsted-Lowry definition?
Answer: As an acid, because it donates a proton to NH3.
When you encounter acid-base reactions, the Brønsted-Lowry definition focuses on proton (H⁺) transfer: acids donate protons, while bases accept them. Look at what's actually happening to each molecule in the reaction.
In this reaction, NH3+H2O⇌NH4++OH−, water starts as H₂O and becomes OH⁻. Notice that water has lost a hydrogen ion (proton) in the process. Since the Brønsted-Lowry definition states that acids are proton donors, water is functioning as an acid by giving up its proton to ammonia. Meanwhile, NH₃ accepts that proton to become NH₄⁺, making ammonia the base.
Looking at the incorrect options: B suggests water accepts a proton from NH₃, but this is backwards—NH₃ doesn't have any protons to give up initially. C calls water a salt, but salts are ionic compounds formed from acid-base neutralization reactions, not participants that lose protons during the reaction. D incorrectly labels water as a neutral spectator, but water is actively participating by donating a proton, not just providing a medium for the reaction.
The correct answer is A because water donates a proton to NH₃.
Study tip: In Brønsted-Lowry problems, trace the hydrogen atoms carefully. The species that loses H⁺ is the acid, regardless of what you might expect from common knowledge. Water can act as either an acid or base depending on what it's reacting with—this is called being amphoteric. - During a titration, a chemist slowly adds a 0.1 M NaOH solution (a strong base) to a 0.1 M HCl solution (a strong acid). What will the pH of the resulting solution be at the equivalence point, where the moles of acid equal the moles of base?
Answer: Exactly 7
When you encounter acid-base titration questions, focus on what happens when equal molar amounts of acid and base react. This tests your understanding of neutralization reactions and the resulting pH.
At the equivalence point in this titration, the strong acid HCl and strong base NaOH react completely in a 1:1 ratio: HCl+NaOH→NaCl+H2O. Since both reactants have equal molarity (0.1 M) and equal molar amounts are present, they neutralize each other completely. The products are salt (NaCl) and water. Sodium chloride is the salt of a strong acid and strong base, making it a neutral salt that doesn't affect the pH of the solution. Therefore, the resulting solution has a pH of exactly 7.
Answer choice (A) "Less than 7" would occur if you had excess acid remaining or if the salt formed were acidic, but neither applies here. Answer choice (B) "Greater than 7" would happen with excess base or a basic salt, which also doesn't occur in this strong acid-strong base titration. Answer choice (D) "Exactly 0" represents a fundamental misunderstanding—this would indicate an extremely acidic solution with [H+]=1 M, not a neutralized solution.
The correct answer is (C) exactly 7.
Study tip: Remember that strong acid + strong base = neutral solution (pH 7) at equivalence. Only weak acid-strong base or strong acid-weak base titrations give pH ≠ 7 at equivalence due to salt hydrolysis. - A cleaning solution is found to have a pH of 11. Which statement accurately describes this solution?
Answer: It is basic and has a lower concentration of H+ ions than OH- ions.
When you encounter pH questions on the HESI, remember that pH is a logarithmic scale measuring hydrogen ion concentration, where values below 7 are acidic, 7 is neutral, and above 7 is basic (alkaline).
A pH of 11 indicates a basic solution. In basic solutions, hydroxide ions (OH⁻) are more abundant than hydrogen ions (H⁺). This happens because bases either release OH⁻ ions directly or accept H⁺ ions from water molecules, leaving excess OH⁻ ions behind. The higher the pH above 7, the more basic the solution becomes.
Looking at the answer choices: Option A incorrectly identifies the solution as acidic. Acidic solutions have pH values below 7, not 11, and they do have higher H⁺ concentrations than OH⁻ concentrations. Option B calls the solution neutral, but neutral solutions have a pH of exactly 7 with equal H⁺ and OH⁻ concentrations. Option D correctly identifies the solution as basic but incorrectly states that H⁺ ions are more concentrated than OH⁻ ions—this is backwards for basic solutions. Option C correctly identifies both characteristics: the solution is basic (pH > 7) and has a lower concentration of H⁺ ions than OH⁻ ions.
For HESI success, memorize this pattern: pH < 7 = acidic (more H⁺), pH = 7 = neutral (equal H⁺ and OH⁻), pH > 7 = basic (more OH⁻). Many students mix up ion concentrations in basic solutions, so always remember that "basic" means "more bases (OH⁻)."
- A solution is prepared with a hydroxide ion [OH-] concentration of 1×10−4 M. Which of the following best describes this solution?
Answer: It is a basic solution with a pH of 10.
When you encounter pH and pOH problems on the HESI, you need to understand the relationship between hydroxide ion concentration, hydrogen ion concentration, and the pH scale. At 25°C, water has the equilibrium constant Kw=[H+][OH−]=1×10−14.
Given that [OH−]=1×10−4 M, you can find the hydrogen ion concentration: [H+]=1×10−41×10−14=1×10−10 M. The pH is calculated as pH=−log[H+]=−log(1×10−10)=10. Since the pH is greater than 7, this solution is basic.
Answer choice B correctly identifies this as a basic solution with pH 10.
Answer choice A incorrectly states the solution is acidic with pH 4. This represents a fundamental misunderstanding—confusing the hydroxide concentration's exponent (-4) with the actual pH value.
Answer choice C incorrectly calls it basic but assigns pH 4. While recognizing that high hydroxide concentration means basic conditions, it makes the same mathematical error as choice A.
Answer choice D incorrectly labels the solution as acidic with pH 10. This contradicts basic chemistry principles since pH values above 7 are always basic, never acidic.
Study tip: Remember that pH+pOH=14 at 25°C. When given [OH−], calculate pOH=−log[OH−], then subtract from 14 to get pH. If pOH<7, the solution is basic; if pOH>7, it's acidic. - If a beaker of pure water at pH 7 is used to dilute a solution of nitric acid (HNO3) with a pH of 1, what will be the resulting effect on the pH of the nitric acid solution?
Answer: The pH will increase, moving towards 7.
When you encounter pH and dilution problems, remember that pH measures hydrogen ion concentration on a logarithmic scale. Adding water to an acidic solution always dilutes the acid, reducing the concentration of hydrogen ions and raising the pH toward neutral.
Here's what happens when you dilute the nitric acid solution: The original solution has a pH of 1, meaning it contains a high concentration of H⁺ ions. When you add pure water (pH 7), you're increasing the total volume while keeping the same amount of acid. This spreads the H⁺ ions over a larger volume, reducing their concentration. Since pH is inversely related to H⁺ concentration, the pH increases, moving closer to 7.
Looking at the wrong answers: Choice A suggests the pH decreases toward 0, which would mean the solution becomes more acidic—this contradicts the basic principle that dilution reduces concentration. Choice C incorrectly assumes that being a strong acid means the pH won't change upon dilution. While HNO₃ is indeed a strong acid (fully ionizes), dilution still affects the concentration of those ions. Choice D suggests the pH will exceed 7, making the solution basic. However, adding neutral water to an acidic solution can only move the pH toward neutral, never past it to the basic side.
For HESI chemistry questions, remember this key principle: dilution always moves pH toward neutral (7). Acidic solutions become less acidic, and basic solutions become less basic, but water alone cannot change an acid to a base or vice versa.
- A student mixes a solution of hydrochloric acid (HCl), a strong acid, with a solution of potassium hydroxide (KOH), a strong base. Assuming the reactants are in stoichiometrically equivalent amounts, what are the primary products of this reaction?
Answer: Potassium chloride (KCl) and water (H2O)
When you encounter acid-base reactions on the HESI, focus on the fundamental principle that acids and bases neutralize each other to form salt and water. This is one of the most predictable reaction types in chemistry.
In this reaction, hydrochloric acid (HCl) donates a hydrogen ion (H⁺), while potassium hydroxide (KOH) donates a hydroxide ion (OH⁻). The complete reaction is: HCl+KOH→KCl+H2O
The H⁺ from the acid combines with the OH⁻ from the base to form water (H₂O), while the remaining ions (K⁺ and Cl⁻) form the salt potassium chloride (KCl). Since both reactants are strong and present in stoichiometrically equivalent amounts, the reaction goes to completion, producing these two products.
Answer A is correct because it identifies both products of this classic acid-base neutralization. Answer B is wrong because potassium hydride and chloric acid aren't formed in simple neutralization reactions—these would require entirely different reaction conditions. Answer C incorrectly suggests hydrogen gas production, which occurs in metal-acid reactions, not acid-base neutralizations, and potassium hypochlorite isn't formed here. Answer D is incomplete because while water does form, it ignores the salt product that always accompanies neutralization reactions.
Remember this pattern: strong acid + strong base = salt + water. The salt is always formed from the metal cation (K⁺) and the acid's anion (Cl⁻). This formula works for virtually all acid-base neutralization problems you'll see on the HESI. - A patient's stomach fluid has a pH of 2. After taking an antacid, the pH of the fluid changes to 4. What is the change in the hydrogen ion concentration ([H+]) in the patient's stomach?
Answer: The [H+] decreased by a factor of 100.
When you encounter pH problems on the HESI exam, remember that pH is a logarithmic scale where each unit represents a 10-fold change in hydrogen ion concentration. The relationship is: [H+]=10−pH
To find the change in hydrogen ion concentration, calculate the [H+] at both pH values. At pH 2: [H+]=10−2. At pH 4: [H+]=10−4.
To determine the factor of change, divide the initial concentration by the final concentration: 10−410−2=10−2−(−4)=102=100
This means the hydrogen ion concentration decreased by a factor of 100, making answer C correct.
Let's examine why the other options are wrong. Answer A suggests the [H+] decreased by a factor of 2, which would be true if pH changed by about 0.3 units, not 2 full units. Answer B states the [H+] increased by a factor of 100, but since pH increased (became less acidic), the [H+] must have decreased, not increased. Answer D claims the [H+] decreased by half, which again would require only a small pH change of about 0.3 units.
Study tip: For HESI pH questions, remember the "rule of 10s" - each pH unit change represents a 10-fold change in [H+]. When pH increases by 2 units, [H+] decreases by 102=100 times. This logarithmic relationship is frequently tested in acid-base problems. - In the Brønsted-Lowry theory, a conjugate acid is formed when a base accepts a proton. What is the conjugate acid of the bicarbonate ion, HCO3−?
Answer: Carbonic acid (H2CO3)
Understanding acid-base chemistry requires mastering the Brønsted-Lowry theory, which defines acids as proton donors and bases as proton acceptors. When dealing with conjugate acid-base pairs, remember that a conjugate acid forms when a base gains a proton (H⁺), while a conjugate base forms when an acid loses a proton.
To find the conjugate acid of bicarbonate ion (HCO3−), you need to determine what happens when this base accepts a proton. Starting with HCO3− and adding H⁺ gives you H2CO3 (carbonic acid). The reaction is: HCO3−+H+→H2CO3
Option C is correct because carbonic acid is exactly what forms when bicarbonate accepts a proton.
Option A (carbonate ion, CO32−) is incorrect because this would be the conjugate base of bicarbonate—what you'd get if bicarbonate lost a proton rather than gained one. Option B (hydroxide ion, OH−) is completely unrelated to the bicarbonate system and represents a different base entirely. Option D (hydrogen ion, H+) is the proton itself, not a conjugate acid formed by accepting a proton.
Remember this pattern: to find a conjugate acid, add H⁺ to the original species; to find a conjugate base, remove H⁺. Also, notice how the charge changes—bicarbonate's -1 charge becomes neutral (0) in carbonic acid after gaining the +1 proton. This charge accounting helps verify your answer. - A patient's blood sample shows a pH of 7.35. If the hydrogen ion concentration increases by a factor of 2, what will be the approximate new pH value?
Answer: The new pH will be approximately 7.05 because the pH decreases by 0.30 units when hydrogen ions double
When hydrogen ion concentration doubles, the pH decreases by log₁₀(2) = 0.30 units. Starting from pH 7.35, the new pH = 7.35 - 0.30 = 7.05. Choice A incorrectly assumes a linear relationship between pH and [H+]. Choice C incorrectly suggests that increased [H+] raises pH. Choice D incorrectly applies the inverse relationship and would result in an impossible pH value above 14.
- A nurse is handling a chemical spill of an unknown substance. The substance feels slippery to the touch and, when tested with litmus paper, turns it blue. These properties are characteristic of which type of substance?
Answer: An alkaline solution
Chemical safety questions on the HESI often test your ability to identify substances based on their physical and chemical properties. When you encounter an unknown chemical, specific characteristics can help you determine what type of substance you're dealing with.
The key clues here are that the substance feels slippery and turns litmus paper blue. These are classic indicators of a basic (alkaline) solution. Bases have a characteristic slippery or soapy feel because they react with oils in your skin to form soap-like compounds. When litmus paper turns blue, it confirms the presence of a base, as bases have a pH greater than 7.
Looking at the wrong answers: A) Strong acids would turn litmus paper red, not blue, and typically don't feel slippery but rather may cause a burning sensation. C) Neutral salt solutions have a pH of 7 and wouldn't change litmus paper color significantly—it would remain its original color. D) Nonpolar solvents like oils or hexane don't affect litmus paper at all since they don't ionize in water, and they typically feel oily rather than slippery in the soap-like way that bases do.
Answer B is correct because alkaline solutions exhibit exactly these properties: they feel slippery due to their ability to saponify fats and oils, and they turn litmus paper blue due to their basic pH.
For HESI chemical safety questions, remember this pattern: red litmus = acid, blue litmus = base, slippery feel = base. Always associate multiple properties together rather than relying on just one indicator.
