Measurements

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AP Chemistry › Measurements

Questions 1 - 10
1

Convert the given value to scientific notation.

Explanation

Scientific notation is used to simplify exceptionally complex numbers and to quickly present the number of significant figures in a given value. The value is converted to an exponent form using base ten, such that only a single-digit term with any given number of decimal places is used to represent the significant figures of the given value. Non-significant zeroes can be omitted from the leading term, and represented only in the base ten exponent.

The given number has five significant figures (100.43), so there will be five digits multiplied by the base ten term.

To generate the single-digit leading term the decimal must be placed after the 1 (1.0043). Then count the digits to the right of the decimal to determine the change in decimal placement (the decimal moves past the two zeroes). Our ten will be raised to the power of two because there are two digits to the right of the final decimal placement.

Our final answer is

2

Consider the following four samples:

of potassium

of lithium

of magnesium

of chlorine gas

Which of the given samples contains the most atoms?

Lithium

Potassium

Chlorine

They all have the same number of atoms

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.

3

Consider the following four samples:

of potassium

of lithium

of magnesium

of chlorine gas

Which of the given samples contains the most atoms?

Lithium

Potassium

Chlorine

They all have the same number of atoms

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.

4

Consider the following four samples:

of potassium

of lithium

of magnesium

of chlorine gas

Which of the given samples contains the most atoms?

Lithium

Potassium

Chlorine

They all have the same number of atoms

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.

5

Convert the given value to scientific notation.

Explanation

Scientific notation is used to simplify exceptionally complex numbers and to quickly present the number of significant figures in a given value. The value is converted to an exponent form using base ten, such that only a single-digit term with any given number of decimal places is used to represent the significant figures of the given value. Non-significant zeroes can be omitted from the leading term, and represented only in the base ten exponent.

The given number has five significant figures (100.43), so there will be five digits multiplied by the base ten term.

To generate the single-digit leading term the decimal must be placed after the 1 (1.0043). Then count the digits to the right of the decimal to determine the change in decimal placement (the decimal moves past the two zeroes). Our ten will be raised to the power of two because there are two digits to the right of the final decimal placement.

Our final answer is

6

Convert the given value to scientific notation.

Explanation

Scientific notation is used to simplify exceptionally complex numbers and to quickly present the number of significant figures in a given value. The value is converted to an exponent form using base ten, such that only a single-digit term with any given number of decimal places is used to represent the significant figures of the given value. Non-significant zeroes can be omitted from the leading term, and represented only in the base ten exponent.

The given number has five significant figures (100.43), so there will be five digits multiplied by the base ten term.

To generate the single-digit leading term the decimal must be placed after the 1 (1.0043). Then count the digits to the right of the decimal to determine the change in decimal placement (the decimal moves past the two zeroes). Our ten will be raised to the power of two because there are two digits to the right of the final decimal placement.

Our final answer is

7

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

How many moles is of ?

Explanation

Use the periodic table to calculate the molecular weight of sodium hydroxide.

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

8

How many moles of carbon are in a sample of atoms?

Explanation

To solve, we need to convert atoms to moles using Avogadro's number:

9

What is the concentration of Ca in a solution of 1 mol CaCl2 in 1 L of distilled water? (M = molarity, m= molality)

1 M

2 M

1 m

2 m

Cannot be determined

Explanation

The definition of molality is moles of solute in 1 kg of the solvent, whereas molarity is the number of moles of solute per 1 L of solutioin. Since 1 mol of CaCl2 is added to 1 L of water, this means that the volume of the final solution is greater than 1 L. Thus, molality is the more accurate concentration determinant, since the solution is probably close to 1 L.

10

What is the concentration of Ca in a solution of 1 mol CaCl2 in 1 L of distilled water? (M = molarity, m= molality)

1 M

2 M

1 m

2 m

Cannot be determined

Explanation

The definition of molality is moles of solute in 1 kg of the solvent, whereas molarity is the number of moles of solute per 1 L of solutioin. Since 1 mol of CaCl2 is added to 1 L of water, this means that the volume of the final solution is greater than 1 L. Thus, molality is the more accurate concentration determinant, since the solution is probably close to 1 L.

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