Chemical Reaction Quiz 2015 Self-Testing Guide DUE day of quiz!
Name: ANSWERS IN BOLD
Students should be able to . . .
Review
Describe a neutral atom.
A neutral atom is an atom with a neutral charge. The negative charge of each electron is balanced by a positive charge from a proton. In other
words, the number of electrons equals the number of protons.
Describe how an atom becomes charged and the name chemists give atoms with a charge.
When an atom loses or gains an electron it is called an ion. If the atom loses 1 or more electrons it becomes positively charged and it called a
cation. When an atom gains 1 or more electrons it becomes negatively charged and it called an anion.
Chemical Reactions
Remember when we saw the cool video with the weird “growing snakes” and placed drops of BTB into a snack bag with salt, baking soda
and the strong chemical calcium chloride:
1. What acronym do we use to describe 5 categories of evidence that a chemical reaction has occurred. We used the acronym SOFT C to remember the 5
categories of evidence that a chemical reaction has occurred.
2. Give an example for each of the 5 letters in the acronym.
Something New – Like when we reacted vinegar and baking soda and gases formed. New gases often appear as bubbles or fizzing.
the vinegar didn’t smell as strong after we reacted it with baking soda.
Odor - like when
Formation of a precipitate - like when we reacted the blue copper sulfate and
the clear ammonia and a blueish-white insoluble product formed. Temperature - when heat is given off (exothermic) like when the contents of the
baggie in our lab turned warm. Sometimes heat is need to break apart the reactant so it feels colder (endothermic) like the cold bottle when we
reacted vinegar and baking soda, Color like when the contents of the baggie in our lab turned yellow. You have to be careful with color. When we
made Kool Aide the mixture turned red, but the color came from the Kool Aide packet not from a chemical reaction.
3. How are physical changes and chemical changes different?
Physical changes just move the matter around or change its size, shape, or state of matter. Chemical changes rearrange the atoms/molecules of the
matter into something new, a new type of matter.
Remember when we teamed up to explore reactions that take in heat (Alka-Seltzer tablet and water) and others that give off heat like
when we reacted hydrogen peroxide using yeast as a catalyst
4. What do scientists call a reaction that produces heat and spreads the heat to the surroundings? What is the most common evidence a student would
notice after this type reaction?
The reaction that spreads heat into the surrounds is called exothermic. The most common evidence of an exothermic reaction is the temperature rises
and/or it feels warmer.
5. What word describes a chemical that just has to be there in order for a reaction to occur? It is not a reactant or a product.
Scientists use the word catalyst to describe a substance that helps the reaction happen; it’s not a reactant or a product. The yeast in the hydrogen
peroxide reaction was a catalyst not a reactant.
6. What do scientists call a reaction that requires heat from the surroundings? What is the most common evidence a student would notice after this type
reaction?
The reaction that requires lots of heat from the surroundings to break apart the reactants is called endothermic. The most common evidence of an
exothermic reaction is the temperature decreases and/or it feels cold.
7. Describe the difference between reactants and products.
Reactants are the chemicals at the start of a chemical reaction and products are the new chemicals at the end. See example in next question.
Remember when we created acetylene gas then lit a spark so it would react rapidly with oxygen to introduce the idea that atoms in
reactants become the atoms in the products
8. Describe the difference between reactants and products.
DUPLICATE OF QUESTION 7
9. If a student reacts CH4 (methane) with O2 (oxygen gas) is it possible to form CO2? How do you know?
Yes it’s possible to form CO2 with this reaction because the carbon and oxygen atoms are available in the reactants.
10. If a student reacts HNO3 with NaHCO3 could the products be NaNO3 + CO2 + H2O? How do you know?
Yes this reaction is possible because the atoms in the reactants equal the atoms in the products. For example there is one atom of nitrogen (n) in the
reactants and one atom of nitrogen in the products.
Remember when we reacted copper sulfate (blue liquid) with ammonia (clear liquid).
11. Can the mixture of 2 solutions, homogenous liquid mixtures containing soluble molecules, produce something that is insoluble? How do you know?
When 2 solutions react it’s possible to form something new, called a precipitate that is insoluble even though the reactant started out soluble. We
reacted the blue copper sulfate and the clear ammonia and a blueish-white insolvable product formed. Not all reactions involving two liquids form a
precipitate.
12. What word do scientists use for an insoluble molecule produced from a reaction of 2 solutions?
A new insoluble product of a reaction between 2 solutions is called a precipitate.
Remember when we reacted baking soda and vinegar and changed the concentration of the vinegar.
13. When baking soda reacts with vinegar, carbonic acid (water and carbon dioxide gas) and sodium acetate are formed. Draw a single circle around the
words that define the reactants and a double circle around the words that define the products of this reaction.
When baking soda reacts with vinegar, carbonic acid (water and carbon dioxide gas) and sodium acetate are formed. Draw a single circle around the
words that define the reactants and a double circle around the words that define the products of this reaction
14. How do the properties of reactants compare to the properties of products? What evidence supports your answer?
Because products are different substances than reactants, they will have different properties. As an example carbonic acid has bubbles because it
contains carbon dioxide gas and acetic acid (vinegar) has no bubbles.
15. What do scientists call a reaction that requires heat from the surroundings? What is the most common evidence a student would notice after this type
reaction?
DUPLICATE OF QUESTION 6
16. If you start a reaction with 25 grams of reactants, what mass of products will you have at the end and how do you know?
The mass of reactants equal the mass of products because of the Law of Conservation, so the mass of products at the end would be 25 grams.
Remember when we reacted copper sulfate (blue liquid) with ammonia (clear liquid).
17. What observable evidence do you see when a precipitate forms?
You are looking for a new solid mixed with the liquid when a precipitate forms.
18. Can the mixture of 2 solutions, homogenous liquid mixtures containing soluble molecules, produce something that is insoluble? How do you know?
DUPLICATE OF QUESTION 11
19. What word do scientists use for an insoluble molecule produced from a reaction of 2 solutions?
DUPLICATE OF QUESTION 12
Remember when we used an Alka-Seltzer tablet in a water bottle with a lid to test whether chemical reactions obey the Law of
Conservation of Mass
20. What evidence do you observe that a chemical reaction occurred?
For this reaction we saw bubbles, heard fizzing and the bottle felt cold on our cheek. Some students wafted the contents and reported a change in
odor.
21. In this lab, what are the reactants?
The reactants were water and the Akla-Seltzer tablet.
22. How does the mass of reactants compare to the mass of products when a reaction obeys the Law of Conservation of Mass?
Based on the Law of Conservation of Mass, the mass of the reactants should be equal to the mass of the products. Reactants become products with
nothing added and nothing left over.
23. Does the Law apply to chemical reactions? How do you know?
Yes, because the actual measured mass of reactants matched or nearly matched the mass of the products, the reaction does obey the Law of
Conservation of Mass.