Practice Test 47 - High School Chemistry

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

A student claims: "Iron is more reactive than copper." In a controlled test, equal-sized pieces of iron and copper were placed into separate beakers containing the same volume of 1.0 M hydrochloric acid at 25°C. Observations: 1) Iron produced bubbles steadily; copper produced no visible bubbles. 2) After 10 minutes, the iron piece looked smaller; the copper piece looked unchanged. 3) Both metals were shiny before being placed in acid. 4) The acid in both beakers was clear at the start. Which statement best evaluates the claim using the evidence?
A student dissolves 10 g of ammonium nitrate in 50 mL of water in a beaker. The water temperature decreases from 22°C to 14°C. Which statement is correct?
Lithium (Li), sodium (Na), and potassium (K) are all in Group 1. They show similar chemical behavior, such as reacting with water and forming $+1$ ions. Which statement best explains why these elements behave similarly?
Which represents the correctly balanced equation (smallest whole-number coefficients)? Fe + O2 → Fe2O3
Students test the research question: How does the amount of solute affect the conductivity of a salt solution? They add different masses of NaCl (0.50 g, 1.00 g, 1.50 g, 2.00 g) to separate beakers, each containing 100 mL of distilled water at 25C. They stir each solution for 2 minutes and then use the same conductivity probe to record conductivity in mS/cm. Which list best describes controlled variables in this investigation?
A student asks: "How does stirring affect how fast table salt dissolves in water?" They add 5.0 g of NaCl to 100 mL of water at 25°C in three beakers. Beaker 1 is not stirred, Beaker 2 is stirred slowly (about 1 stir per second), and Beaker 3 is stirred quickly (about 3 stirs per second). They record the time until no solid salt remains. What is being measured as the outcome?
A small food company is testing whether adding vitamin C (ascorbic acid) to cut apples prevents browning during packaging. Browning could be a chemical change (oxidation), which affects product quality. Design an investigation to answer: Does treating apple slices with vitamin C solution reduce the chemical change that causes browning? Which design is best?
Students investigate the question: How does stirring speed affect how quickly salt dissolves? They add 5.0 g of table salt (NaCl) to 100 mL of water at 25C in identical beakers. For three trials, they stir using a glass rod at 0 stirs per second (no stirring), 1 stir per second, and 2 stirs per second, and record the time until no solid crystals remain. Which factors must be kept the same for a fair test? (Choose the best list of controlled variables.)
A team chooses a zinc-plated steel bolt for an outdoor bike rack because it is inexpensive and "rust-resistant." After 2 months near the ocean, inspection shows rust forming first at scratched areas where the zinc coating is damaged; bolts with intact coating show little rust. Which refinement is most directly supported by the evidence to improve corrosion resistance in the real environment?
A science museum is building an interactive display with a sealed container of dilute hydrogen peroxide (3%) for a safe demonstration (no direct contact). Requirements: container must not catalyze rapid decomposition (critical for shelf life), should be shatter-resistant for public safety, and cost should be reasonable. Materials: - Clear glass: chemically compatible; good barrier; can shatter. - HDPE plastic: commonly used for peroxide; shatter-resistant; slightly more permeable to gases over long times. - Iron/steel: can catalyze peroxide decomposition; strong; low cost.
In the alpha decay equation $^{238}_{92}\mathrm{U} \rightarrow {}^{234}_{90}\mathrm{Th} + {}^{4}_{2}\mathrm{He},$ what happens to the atomic number of the nucleus after the decay?
Which statement best explains why nuclear reactions typically release much more energy per atom than chemical reactions, without doing any calculations?
A food-processing plant needed new piping to carry a warm ( $45^\circ$ C) cleaning solution containing dilute sodium hydroxide (a base). Engineers chose stainless steel (304) instead of plain carbon steel. After 18 months, inspections showed no pitting or rust in the stainless steel lines, while a short carbon-steel test section developed rust and rough interior surfaces within 6 weeks. Which justification best supports the stainless-steel choice?
A news article says that a small uranium fuel pellet can produce as much energy as a large pile of coal. Without doing any calculations, what is the best scientific reason this can be true when comparing energy per unit mass?
Neon (Ne) has electron configuration 1s2 2s2 2p6 and sodium (Na) has electron configuration [Ne]3s1. Neon has a much higher first ionization energy than sodium. Which feature of the electron configurations best explains this difference?
Three elements are in the same group (group 1, alkali metals): lithium (Li) is in period 2, sodium (Na) is in period 3, and potassium (K) is in period 4. Which element has the largest atomic radius?
Sodium (Na) is a Group 1 element with atomic number 11. A neutral sodium atom becomes a sodium ion, Na⁺. Which statement best explains why Na forms Na⁺?
A student mixes two solutions in a sealed jar. Reaction: $\mathrm{AgNO_3(aq) + NaCl(aq) \rightarrow AgCl(s) + NaNO_3(aq)}$ . Masses of reactant solutions added: - $\mathrm{AgNO_3}$ solution: 40 g - $\mathrm{NaCl}$ solution: 40 g The jar is sealed before mixing and remains sealed. After the precipitate forms, which total product mass is expected (not including the jar)?
A reaction is observed to be endothermic (it makes the surroundings cooler). In terms of bond changes, which must be true overall?
Hydrogen peroxide solution (H $_2$ O $_2$ ) slowly decomposes to form oxygen gas. A student compares two identical beakers containing the same volume and concentration of H $_2$ O $_2$ . Beaker 1 is kept at $10^\circ\text{C}$ and Beaker 2 is kept at $30^\circ\text{C}$ . No catalyst is added. Which statement best predicts the rate difference and the reason?

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