1/10 easy chem
A chemical system undergoes a closed-system transformation in which all reactant particles are rearranged into product particles. If the initial total mass is 73.6 g, what is the final total mass?
73.6 g
A liquid has a density of 0.8 g/mL. Would a piece of material with a density of 1.2 g/mL sink or float in it?
Sink, because the object's density is greater than the liquid's.
An atom has 15 protons, 16 neutrons, and 18 electrons.
What is its element, mass number, and charge?
Phosphorus, 31, −3
A substance has a pH of 3. Another has a pH of 5.
How many times greater is the hydrogen-ion concentration of the pH 3 solution compared with the pH 5 solution?
100 times
An atom has 20 protons, 20 neutrons, and 18 electrons.
Without using the periodic table, determine:
An atom contains 11 protons, 12 neutrons, and 10 electrons.
What is its mass number and charge?
Mass number = 23; charge = +1
An atom has 19 protons and 18 electrons.
What element is it, and what is its charge?
Potassium (K), +1
Two objects have the same volume.
Object A has a mass of 20 g and Object B has a mass of 50 g.
Which has greater density?
Object B
An atom has 2 fewer electrons than protons.
What type of ion is it?
+2 cation
A student heats a solid substance. At first, its temperature increases. Then, for several minutes, the temperature stays exactly the same even though heating continues. After this, the temperature starts increasing again.
Using the particle model, explain what is happening during the period when the temperature stays constant.
The substance is changing state. The energy supplied is being used to overcome forces between particles, rather than increasing their kinetic energy. Therefore, the temperature remains constant until the change of state is complete.
A substance has a mass of 72 g and a volume of 24 mL.
What is its density?
3 g/mL
Why does increasing temperature generally cause particles in a substance to move faster?
: Temperature is related to the particles' average kinetic energy
A student claims that a substance must be an element because it looks completely uniform.
why is ts false?
A mixture can also appear uniform; a homogeneous mixture can look like one substance.
Why are noble gases generally less reactive than elements in many other groups?
Why are noble gases generally less reactive than elements in many other groups?
You are given a pure substance that contains only two types of atoms.
You heat it strongly and obtain two completely different substances, neither of which can be broken down chemically into simpler substances.
Is the original substance an element, mixture, or compound?
Explain how you know, and explain why the two products prove your answer.
It is a compound. A compound contains different elements chemically bonded together. Heating causes a chemical decomposition, producing simpler substances that are elements. A mixture would not require chemical decomposition to separate its components.
An atom has an atomic number of 16 and a mass number of 34.
How many protons, neutrons, and electrons does a neutral atom have?
Answer: 16 protons, 18 neutrons, 16 electrons
A student heats a solid and observes that it becomes a liquid. Then they continue heating it until it becomes a gas.(both changes)
Melting → vaporization
A neutral atom has 24 electrons.
How many protons does it have?
24 (drop chem if u got ts wrong)
A compound contains 2 hydrogen atoms for every 1 oxygen atom.
If you have 18 hydrogen atoms, how many oxygen atoms are needed?
9 oxygen atoms
Four metals are tested:
Arrange the four metals from most reactive to least reactive.
Then explain why the final observation is consistent with your answer rather than contradictory.
A > B > C > D
A metal can displace another metal only if it is more reactive. Since A > B > C > D, D cannot displace A, so the observation is exactly what we would expect.
A student says:
"If I cut a piece of gold in half, I have created a new substance."
Explain why the student is wrong.
Cutting gold changes its size/shape but not its chemical identity, so it's a physical change.
A sample has a mass of 90 g and density of 6 g/mL.
What is its volume?
15 mL
A chemical reaction occurs in an open container. The measured mass afterward is lower than before.
Does this necessarily violate conservation of mass? Explain.
No. Some matter may have escaped as a gas. The total mass would still be conserved if you included everything that left the container.
A reaction begins with 15 g of A and 25 g of B.
It produces 30 g of C and an unknown amount of D.
How much D was produced?
10 g
You are given a mixture containing iron filings, sand, salt, and water.
You must obtain each component separately, with each substance as pure as reasonably possible.
You have access to a magnet, filter paper, evaporating basin, and distillation apparatus.
What is the correct order of separation techniques, and explain why changing the order could make the separation less effective?
The order matters because filtration cannot remove dissolved salt, and simply evaporating the solution would lose the water rather than allowing it to be collected. Removing the iron first also prevents it from interfering with later separation steps.