Given what we know, we can confirm that as with any experiment, the control variable will be the one that through each trial of the experiment, no matter how many times it is performed, stays constant.
<h3>What is a controlled variable?</h3>
- A variable that remains constant through an experiment.
- They are used to compare results to the normal condition.
- They are also used to isolate the changes to one factor at a time and thus know its exact effects on the outcome.
- This increases the accuracy of the data and the subsequent conclusion.
Therefore, we can confirm that if a variable stays constant through each phase and trial of an experiment, it is considered to be a controlled variable and is useful in order to increase the accuracy of the conclusion.
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Answer:

Explanation:
We are asked to find how many moles of sodium carbonate are in 57.3 grams of the substance.
Carbonate is CO₃ and has an oxidation number of -2. Sodium is Na and has an oxidation number of +1. There must be 2 moles of sodium so the charge of the sodium balances the charge of the carbonate. The formula is Na₂CO₃.
We will convert grams to moles using the molar mass or the mass of 1 mole of a substance. They are found on the Periodic Table as the atomic masses, but the units are grams per mole instead of atomic mass units. Look up the molar masses of the individual elements.
- Na: 22.9897693 g/mol
- C: 12.011 g/mol
- O: 15.999 g/mol
Remember the formula contains subscripts. There are multiple moles of some elements in 1 mole of the compound. We multiply the element's molar mass by the subscript after it, then add everything together.
- Na₂ = 22.9897693 * 2= 45.9795386 g/mol
- O₃ = 15.999 * 3= 47.997 g/mol
- Na₂CO₃= 45.9795386 + 12.011 + 47.997 =105.9875386 g/mol
We will convert using dimensional analysis. Set up a ratio using the molar mass.

We are converting 57.3 grams to moles, so we multiply by this value.

Flip the ratio so the units of grams of sodium carbonate cancel.




The original measurement of moles has 3 significant figures, so our answer must have the same. For the number we found that is the thousandth place. The 6 in the ten-thousandth place to the right tells us to round the 0 up to a 1.

There are approximately <u>0.541 moles of sodium carbonate</u> in 57.3 grams.
Answer: I did the research myself since I couldn’t find the answers.
Physical change:
Wax melting from applied heat
Grinding wheat to make flour
Adding copper with gold to make jewelry
Chemical Reaction:
Growth of a seed into a seedling
Making caramel by burning sugar
Tarnishing of silver
Explanation:
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