Practice Test 48 - High School Chemistry

20 questions. Answer them in any order, then submit to see your score and every explanation.

A student mixes a clear household cleaner with another clear liquid in a cup. Soon, a strong new odor is noticed and bubbles begin to form throughout the liquid (the cup is not being heated). Which observations indicate a chemical reaction may be occurring?
Consider the balanced equation: $2H_2 + O_2 \rightarrow 2H_2O$ If $5.0 \text{ mol}$ of $H_2$ react completely, how many moles of $H_2O$ are formed?
Fluorine (F), chlorine (Cl), and bromine (Br) are all in Group 17 and often form −1 ions. Which statement best explains this similarity using atomic structure?
A student performs a reaction in a beaker and observes that the beaker becomes noticeably warm. The reaction's enthalpy change is consistent with $\Delta H = -90\ \mathrm{kJ}$ . Which explanation best matches this observation?
What is the electron configuration of the sodium ion, Na⁺ (sodium has atomic number 11)?
A class discusses energy density (energy per kilogram of fuel). They hear that burning 1 kg of coal releases on the order of $\sim 3\times 10^7$ J, while fissioning 1 kg of uranium releases on the order of $\sim 8\times 10^{13}$ J. Without doing detailed calculations, what is the best qualitative conclusion?
A student tested how the concentration of hydrochloric acid affects the time for a fixed piece of limestone (CaCO $_3$ ) to stop producing bubbles. Each trial used the same mass of CaCO $_3$ (1.50 g) and the same volume of acid (20.0 mL). Three trials were run at each concentration. Which conclusion is best supported by the average times shown?
A concentration-versus-time graph shows product concentration $[P]$ increasing quickly at first and then increasing more slowly until it reaches a plateau. When is the reaction producing product at the fastest rate?
Two students perform the same reaction: Alka-Seltzer tablet in 200 mL of water. They use the same cup, same water volume, and same tablet brand. Student 1 uses cold water (5°C) and sees gentle bubbling for about 3 minutes. Student 2 uses warm water (35°C) and sees rapid bubbling that finishes in about 1 minute. What is the best collision-theory explanation for the faster reaction in warm water?
A student mixes 10 mL of vinegar with a small spoonful of baking soda in a flask. Observations: - Immediate vigorous bubbling and foaming occurs. - The flask feels cooler; temperature drops from $23.5^\circ\text{C}$ to $19.0^\circ\text{C}$ . - After bubbling stops, the mixture is still liquid and looks slightly cloudy. - The total mass of the closed flask system stays the same (measured with a balloon sealing the top): 85.20 g before, 85.20 g after. Did a chemical reaction occur? Choose the best CER justification.
Neon (Ne) has electron configuration $1s^2\,2s^2\,2p^6$ and is very unreactive under normal conditions. Which structural feature best explains neon's lack of reactivity?
Students compare metal reactivity by placing three separate metal strips (zinc, iron, and copper), each cut to 3.0 cm d7 1.0 cm, into three beakers containing 50.0 mL of 2.0 M HCl at room temperature. They observe the reaction for 5 minutes and count the number of gas bubbles produced in 30 seconds at the 1-minute mark. What is the independent variable in this investigation?
Chlorine (Cl) is a group 17 element with atomic number 17 and an electron configuration ending in $3s^2\,3p^5$ . It commonly forms the chloride ion Cl⁻. Which choice correctly explains the change from Cl to Cl⁻?
Consider the reaction $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$ If you start with $3.0\,\text{mol}$ of $\text{H}_2$ and $1.0\,\text{mol}$ of $\text{O}_2$ , which reactant is the limiting reactant (runs out first)?
Ammonia forms according to $\text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3.$ What is the mole ratio of $\text{NH}_3$ to $\text{H}_2$ ?
A student combines two colorless liquids in a cup. The mixture begins fizzing (not boiling), and after a minute the fizzing slows and a yellow color remains. Which combination of evidence best indicates new substances formed?
A student investigates: How does the amount of solute affect the boiling point of water? The student heats 200 mL of distilled water in the same beaker on the same hot plate setting each time. In Trial 1, they add 0.0 g NaCl; in Trial 2, they add 5.0 g NaCl; in Trial 3, they add 10.0 g NaCl. They stir each solution the same way and record the temperature (in C) when a steady rolling boil is reached. What is being measured as the outcome of the experiment?
Hydrogen and oxygen react in a sealed container: $\mathrm{2H_2(g) + O_2(g) \rightarrow 2H_2O(l)}$ . A student starts with 8 g of hydrogen gas and 64 g of oxygen gas in the sealed container. After the reaction goes to completion, what should be the mass of liquid water formed (ignoring the mass of the container)?
A teacher says: "Chemical reactions (like combustion and metabolism) involve rearranging electrons in bonds, while nuclear reactions (like fission, fusion, and radioactive decay) involve changes in the nucleus." Which choice best connects this difference to the energy scale difference?
A manufacturer switched from natural rubber gaskets to silicone rubber gaskets for sealing a household steam cleaner. The device operates around $120\,^{\circ}\mathrm{C}$ and uses water plus small amounts of detergent. In testing, natural rubber gaskets became brittle and leaked after 40 hours, while silicone gaskets maintained flexibility and sealed for 200 hours with no leaks. Which justification best supports the switch?

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