High School Chemistry : Using Moles

研究概念,例子问题&解释for High School Chemistry

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Example Questions

Example Question #1 :Using Moles

Consider the following four samples:

of potassium

of lithium

of magnesium

of chlorine gas

Which of the given samples contains the most atoms?

Possible Answers:

Chlorine

Lithium

They all have the same number of atoms

Potassium

Correct answer:

Lithium

Explanation:

It is important to note that the mass of a sample does not tell you the amount of atoms in the sample. The number of atoms in a sample is dependent on the number moles in a sample, given by Avogadro's number. Here is the number of moles for each sample:

Remember that chlorine is a diatomic mass, so each molecules contains two atoms. This doubles the molar mass for the conversion.

The sample with the greatest number of moles will also contain the most atoms. In this case, the sample of lithium results in the largest number of moles and, thus, the greatest number of atoms.

Example Question #2 :Using Moles

Consider the reaction above. If you start withof potassium bromide, how many moles of bromine are produced? How many molecules is this equal to?

Possible Answers:

Correct answer:

Explanation:

In the chemical equation, the ratio of potassium bromide to bromine is 2:1, so for every 2 moles of, 1 mole ofis produced. Therefore, if we start with 4 moles of, we get 2 moles of. The number of molecules is equal to the number of moles times Avogadro's Number. Since we've determined the number of moles to be 2, the number of molecules is:

Example Question #3 :Using Moles

Convert the following amount from grams (g) to moles (m)

How many moles isof?

Possible Answers:

Correct answer:

Explanation:

使用元素周期表来计算分子weight of sodium hydroxide.

Next, use dimensional analysis to find the number of moles.

Example Question #4 :Using Moles

How many moles ofare present inof the substance?

Possible Answers:

Correct answer:

Explanation:

The molecular weight of carbon dioxide is, meaning inof, there areof the substance.

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