Practice Test 5 - High School Chemistry

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

Which element (atomic number 1-20) has the electron configuration 1s² 2s² 2p⁶ 3s² 3p¹?
Consider the balanced equation: $2KClO_3 \rightarrow 2KCl + 3O_2$ If $4.0\ \text{mol}$ of $KClO_3$ decompose completely, how many moles of $O_2$ are produced?
A teacher is choosing the safest alkali metal (Group 1) for a quick water-reaction demonstration using very small pieces. The options are sodium (Na, Period 3), potassium (K, Period 4), and rubidium (Rb, Period 5). Which is expected to be least reactive with water?
A country is expanding nuclear power to reduce greenhouse gas emissions. Nuclear plants can provide steady electricity with low CO2 emissions during operation and require relatively small amounts of fuel. Concerns include the need to store high-level radioactive waste for very long times, the possibility of accidents, and the fact that some nuclear technologies and materials could be misused to support weapons programs. Which statement best reflects a balanced, informed view?
Calcium (Ca, atomic number 20) is a group 2 metal and commonly forms Ca. Which explanation best justifies this ion charge?
Sodium has electron configuration [Ne]3s1 and chlorine has electron configuration [Ne]3s2 3p5. Both are in period 3 (same number of shells). Chlorine has a smaller atomic radius than sodium. Which explanation best uses electron configuration to account for this trend?
Neon (Ne) is used in bright advertising signs and is very unreactive. Neon is in Group 18 (noble gases). Which justification best explains neon's low chemical reactivity?
Balance the equation using the smallest whole-number coefficients: Ca(OH)2 + HCl → CaCl2 + H2O
Sulfur trioxide forms from sulfur dioxide and oxygen: $\mathrm{2SO_2 + O_2 \rightarrow 2SO_3}$ According to the coefficients, how many moles of sulfur trioxide ( $\mathrm{SO_3}$ ) form per 1 mol of oxygen gas ( $\mathrm{O_2}$ )?
An ion has 13 protons, 14 neutrons, and 10 electrons. What is the charge of the ion?
A student predicts that oxygen (O) will form a $2-$ ion more readily than nitrogen (N) will form a $3-$ ion. Both are in Period 2, with N in Group 15 and O in Group 16. Which justification best supports the student's prediction?
For the neutral isotope ²³Na (sodium-23), how many protons, neutrons, and electrons are in the atom?
Aluminum (Al) has electron configuration $[Ne]3s^2\,3p^1$ and silicon (Si) has electron configuration $[Ne]3s^2\,3p^2$ . Silicon has a smaller atomic radius than aluminum. Which explanation best uses electron configuration to account for this trend?
Three alkali metals (Group 1)—lithium (Li, Period 2), sodium (Na, Period 3), and potassium (K, Period 4)—are each dropped into separate beakers of cold water. Which metal is expected to react most vigorously with water based on periodic position?
Magnesium oxide forms by $\,2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}\,$ . If you start with $6.0\ \text{mol Mg}$ and $2.0\ \text{mol O}_2$ , which reactant is in excess (left over after the reaction stops)?
An energy profile diagram for a single-step reaction starts at the reactant energy level, rises to a peak, and then drops to the product energy level. Which label belongs at the peak of the curve?
A student mixes 25 mL of clear Solution A with 25 mL of clear Solution B in a foam cup. The student records observations before and after mixing: - The mixture turns cloudy within 10 seconds. - A white solid settles to the bottom after 5 minutes. - The temperature changes from $22.0^\circ\text{C}$ to $22.6^\circ\text{C}$ . - No bubbling is observed. Based on the observations, did a chemical reaction occur? Choose the justification that best supports your conclusion using a Claim–Evidence–Reasoning (CER) argument.
Ammonia can be made by the balanced equation $\mathrm{N_2 + 3H_2 \rightarrow 2NH_3}$ According to the coefficients, how many moles of $\mathrm{H_2}$ react with $ 1 $ mol of $\mathrm{N_2}$ ?
An instant cold pack works because dissolving ammonium nitrate in water has $\Delta H = +25\ \text{kJ/mol}$ . Which observation is most consistent with this $\Delta H$ value?
A student places a small piece of chalk into a cup of an acidic liquid. The chalk slowly gets smaller, and steady bubbling is seen on its surface. Which observation is the clearest evidence that a chemical reaction is happening?

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