Question 1
which of the following describes the treatment in an investigation?
a controlled test designed to answer a question or solve a problem
the factor that responds to a change
the factor that is kept constant
the factor that is changed in order to observe a response
question 2
which statement best describes an independent variable?
the variable that responds to change in an investigation
the variable you change in an investigation
the effect in a cause effect relationship
the factor that can never change in an investigation
question 3
liam did an investigation to see how water temperature affects the amount of salt that will dissolve in the water. he filled 4 beakers with exactly 100 milliliters of water each. he then heated each beaker to a different temperature and tested salt solubility at each different temperature. what was liam's independent variable?
amount of water in each beaker
the number of beakers
the amount of salt that dissolved in each beaker
the temperature of the water in each beaker
question 4
which of the following is an example of a treatment?
plants response to changes in temperature
changes made to the temperature of a greenhouse
the kind of soil the plants are in
question 5
jose is curious about which home remedy removes skunk smell from his dog. which of the following is a variable that must be kept constant?
how well the skunk smell is removed.
the home remedy used
the breed of dog
question 6
it is not important to make sure that all variables other than the independent variable are kept constant.
true false
question 7
in order to determine whether or not a substance is an acid or a base, you may stick your finger in the container and make your decision based on whether or not your finger feels slippery.
true false
question 8
a poison hazard symbol means your should not let chemicals contact your skin, ingest or inhale the substance.
true false
question 9
repeating an experiment is important because
you form a hypothesis
it proves the hypothesis is correct
it reduces the chance of error
question 10
when using repeated trials during a scientific investigation, scientists should find the average of their data for use in their final report.
true
false

Experiment: effect of solution concentration on reaction rate you have learned that as the concentration of reactants increases, there will most likely be a greater number of collisions, and hence increase the rate of a reaction. in this experiment, you will see a demonstration of this, with a twist. there will be three reactions going on in this experiment. objectives determine how solution concentration can affect the rate of a reaction. the first reaction will be a reaction of the iodide ion (i-1) with hydrogen peroxide (h2o2) in an acidic solution. this reaction produces a slightly orange solution. in our experiment, we will add some orange food coloring to make this solution more orange. 2 h+ (aq) + 2 i- (aq) + h2o2 (aq) ⟶ i2 (aq) + 2 h2o (l) the next reaction will be between the iodine and starch i2 + starch ⟶ i2-starch complex (blue-black) so, when starch is added to the iodine solution made from the first reaction, the solution will turn black immediately, so it is difficult to find the rate of reaction. in order to be able to time this reaction, you will slow it down with another reaction. adding ascorbic acid will react with the iodine, reducing the concentration of the iodine available to react with the starch. c6h8o6 (aq) + i2 (aq) ⟶ 2i- (aq) + c6h6o6 (aq) + 2 h+ (aq) when the ascorbic acid is used up, the remaining iodine molecules can react with the starch and form the black color. the more ascorbic acid you add, the slower the reaction to form the iodine-starch complex will be. use your data and observations to complete the assignment. analysis and conclusions submit your data and the answers to these questions in the essay box below. what was your hypothesis? plot your data as drops of ascorbic acid vs. time. as the concentration of ascorbic acid was increased, did the rate of the formation of the iodine-starch complex increase or decrease? explain your answer in terms of the chemical reactions involved. was your hypothesis correct? make a general rule about the effects of concentration of reactants on reaction rates. for practice, the molecular formula for ascorbic acid is c6h8o6, and you used 6 g in this experiment, calculate the molarity of the ascorbic acid. now calculate the concentration in moles per drop (assume 1 ml = 20 drops).