Chemical Formulas
How many different elements are represented in the formula NaHCO₃? (name each as well)
4 elements: sodium, hydrogen, carbon, and oxygen.
A glass jar shatters on the floor. Is this a physical or chemical change? Why?
Physical change. Its size and shape change, but the material remains glass
Which has greater average particle kinetic energy: water at 15°C or water at 60°C?
Water at 60°C.
What is the name of a substance that gets dissolved in a solvent?
A solute.
Name one action that generally increases the rate at which a solid dissolves in water.
Stirring, increasing water temperature, or crushing the solid.
How many total atoms are represented in Mg(OH)₂? (Include Math)
5 atoms: 1 Mg + 2 O + 2 H.
A bicycle chain develops reddish-brown rust after being left in the rain. Identify the type of change.
Chemical change. Iron reacts with oxygen and forms rust.
A warm metal spoon is placed in cold water. Which direction does thermal energy flow?
From the warmer spoon to the colder water.
A student mixes powdered lemonade into water. Identify the solvent and solute.
Water is the solvent; dissolved lemonade powder is the solute.
Why does finely crushed rock salt usually dissolve faster than a large piece of the same mass?
Crushing increases total exposed surface area, allowing more contact with the solvent.
Which compound contains more hydrogen atoms, NH₃ or CH₄? How many more?
CH₄ contains 4 hydrogen atoms, one more than NH₃.
Two clear liquids are combined and a solid suddenly appears. What is the solid called, and what might it indicate?
A precipitate. Its formation is evidence that a chemical reaction may have occurred.
A liquid cools from 75°C to 30°C. Describe what happens to the average kinetic energy of its particles.
It decreases; particles have less average kinetic energy at the lower temperature.
A student dissolves 5 g of salt in 100 mL of water. Another dissolves 15 g in 100 mL. Which is more concentrated?
The second solution, assuming both amounts dissolve completely.
A student dissolves identical amounts of salt in 15°C and 65°C water, stirring both equally. Predict which dissolves faster and explain why.
Generally, the 65°C water, because higher temperature increases particle motion and the rate of dissolution.
How many total atoms are represented in 3CaCO₃?
15 atoms. One CaCO₃ unit has 5 atoms; 3 × 5 = 15.
A candle's wax melts while the wick burns. Identify one physical change and one chemical change.
Melting wax is physical; combustion of the wick or wax vapor is chemical.
Two identical metal blocks begin at 80°C and 20°C. After touching for a while in an insulated container, both reach 50°C. Explain why.
Thermal energy moves from the hotter block to the cooler block until they reach thermal equilibrium.
Both cups contain 10 g of dissolved sugar. Cup A contains 100 mL of solution and Cup B contains 250 mL of solution. Which is more dilute? Explain.
Cup B. The same amount of sugar is distributed throughout a larger volume of solution.
Two cups have equal amounts of water at the same temperature. One cup is stirred continuously; the other is not. Explain why the stirred cup will usually dissolve a soluble solid faster.
Stirring continually brings fresh solvent into contact with the solid and carries dissolved material away from its surface.
Compare 2Al₂O₃ and 3CO₂. Which contains more total atoms, and by how many?
2Al₂O₃ has 10 atoms; 3CO₂ has 9. The first contains 1 more atom.
A student claims that every color change proves a chemical reaction occurred. Explain why the claim is inaccurate and give a counterexample.
A color change alone is not proof. An object can look a different color under different lighting without forming a new substance.
A student places an ice cube into a glass of warm water.
What will happen to the particles motion in the Ice cube
Bonus (100 Points): Is the melting ice a physical or chemical change? Explain why.
Thermal energy will cause the particles to speed up as they go into a liquid state of matter
Physical change, because the ice changes from a solid to a liquid without forming a new substance.
True or False: All solutions are mixtures
False, explain please Mr. Vouffo
A sliced apple is left uncovered and its surface turns brown. Make a claim about the type of change, give evidence, and explain your reasoning.
Claim: chemical change. Evidence: the exposed apple surface turns brown over time. Reasoning: browning can result from oxidation reactions that produce substances with different properties.