High School Chemistry : Measurements

Study concepts, example questions & explanations for High School Chemistry

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Example Questions

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Example Question #1 : Units

What unit will be used to denote temperature in thermochemistry?

Possible Answers:

Fahrenheit

Kelvin

Celsius or Kelvin

Joules

Celsius

Correct answer:

Kelvin

Explanation:

Temperature is the measure of the average kinetic energy of a system. Kelvin is the SI unit for temperature, and must be used because it is the only scale that does not have any negative numbers possible. At zero Kelvin (absolute zero) and there is absolutely no movement in the system, down to the atomic level.

While temperature is a means of measuring energy in a system, actual heat energy has the unit Joules.

Example Question #1 : Units

Which of the following measurements contains 4 significant figures?

Possible Answers:

Correct answer:

Explanation:

1. Any digit with a value 1-9 is always a significant figure

2. Any 0 between two digits 1-9 is always significant

3. If a number is greater than 1 and does not have a decimal point a 0 at the end is not significant because it is a tailing zero

4. If a number is less than 1 any 0 before a digit 1-9 is not significant because it is a leading zero

5. If there is a decimal point in any number, any 0 that follows a non-zero digit is always significant.

Thus,  has 4 significant figures. The first 0 is not significant because of rule 4. The digits 1, 9, and 6 are always significant (rule 1) and the last 0 is also significant because there is a decimal point and that 0 follows a non-zero digit (rule 5).

Example Question #1 : Measurements

Which has the larger unit listed first?

Possible Answers:

Kilojoule and megajoule

Decaliter and kiloliter

Picometer and millimeter

Microsecond and nanosecond

Centigram and decigram

Correct answer:

Microsecond and nanosecond

Explanation:

The following prefixes are ranked in order from largest to smallest with the power of 10 that the unit represents: peta (P)  > tera (T)  > giga (G)  > mega (M)  > kilo (k)  > hecta (H)  > deca (D)  > unit > deci (d)  > centi (c)  > milli (m)  > micro   > nano (n)  > pico (p)  > femto (f) . Thus a microsecond is one thousand times longer than a nanosecond.

Example Question #1 : High School Chemistry

The measurement of  is equal to which of the following?

Possible Answers:

Correct answer:

Explanation:

Units in the metric system can be converted using the correct factor of 10.

Example Question #1 : Using Si Units

A certain metal is weighed on a balance in a weighing boat. Before the metal is added, the mass of the weigh boat is recorded at . The final mass of the weigh boat and the metal is . The metal is added to a graduated cylinder filled with water to . After the metal is added to the water the graduated cylinder reads .

What is the density of the metal?

Possible Answers:

Correct answer:

Explanation:

Density is equal to the mass of the object divided by the volume.

The mass of the metal is figured out by taking the mass of the metal and the weighboat  and subtracting the weighboat 

The volume of the water is calculated by the displacement of the water so take the final volume and subtract the initial volume.

The density of the metal is calculated by taking the mass divided by the volume.

  after rounding to 3 significant figures.

Example Question #1 : High School Chemistry

An object is measured to be  tall. How tall is the object in inches? 

Possible Answers:

Correct answer:

Explanation:

You must use equalities and dimensional analysis to solve for the correct answer:

Each equality allows you to write a conversion factor 2 ways: 

Example:  can be written as 

  and 

To cancel out units if there is a unit on top it must be cancelled out by the same unit on the bottom.

To solve you must cancel out units until you get to the proper unit

Example Question #1 : High School Chemistry

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:

They all have the same number of atoms

Chlorine

Lithium

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 #1 : Using Moles

Consider the reaction above. If you start with  of 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 of  is 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 #1 : Using Moles

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

How many moles is  of ?

Possible Answers:

Correct answer:

Explanation:

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

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

Example Question #1 : Units

How many moles of  are present in  of the substance?

Possible Answers:

Correct answer:

Explanation:

The molecular weight of carbon dioxide is , meaning in  of , there are  of the substance.

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