Chemistry Quiz

Question 1

Compounds

Answer 1

Chemical combination of different elements in fixed ratio of atoms

Question 2

Stoichiometric coefficients

Answer 2

Number of units (particles) in a reaction equation

Question 3

Homogeneous mixture

Answer 3

2 or more substances mixed with uniform properties and composition. (looks like pure substance)

Question 4

Heterogeneous mixture

Answer 4

2 or more substances mixed with different properties and composition (you see 2 substances)

Question 5

Diffusion

Answer 5

evenly distribution of particles over space as result of random movement of the particles (fluids and gasses)

Question 6

Changes of state

Answer 6

melting-freezing; evaporating-condensing; sublimation-deposition

Question 7

Avogadro’s constant

Answer 7

6.02x1023, is the number of particles in one mole of a substance

Question 8

Relative atomic mass,

Answer 8

Ar is the weighed average of 1 atom of an element relative to 1/12 of an atom of C-12

Question 9

Water of crystallisation

Answer 9

ratio of chemically bonded water molecules to salt ions

Question 10

Concentration

Answer 10

the amount of solute per unit of volume of solution

Question 11

Formula, empirical

Answer 11

The formula obtained by experiment, showing the simplest whole number ratio of atoms of each element in a particle of a substance

Question 12

Formula, molecular

Answer 12

The formula showing the actual number of atoms of each element in a particle of a substance.

Question 13

Uncertainty

Answer 13

An estimate of the range of values within which the true value of a measurement is expected to be. It is normally expressed as a range of values such as 27.0 ± 0.2

Question 14

Significant figures

Answer 14

The number of significant figures in a measurement is the number of digits that are known for certain plus the first uncertain one.

Question 15

Random errors

Answer 15

Random errors in thermochemistry are caused by uncertainties in the readability of the measuring instruments and the effects of changes in the surroundings, such as temperature variations.

Question 16

Systematic error

Answer 16

These occur when there is an error in the experimental procedure, such as heat losses in an exothermic reaction which lead to smaller temperature changes.

Question 17

Repeatability

Answer 17

Experiments are repeatable if the same person duplicates the experiment with the same results.

Question 18

Reproducibility

Answer 18

Experiments are reproducible if several experimentalists duplicate the results.

Question 19

Accuracy

Answer 19

The accuracy of a result is a measure of how close it is to some accepted or literature value. If an experiment is accurate then the systematic error is small.

Question 20

Precision

Answer 20

Precise measurements have small random errors and are reproducible in repeated trials.

Question 21

Percentage uncertainties

Answer 21

The absolute uncertainty expressed as a percentage of the measured value.
Percentage uncertainty = (absolute uncertainty/measured value) * 100%

Question 22

Absolute uncertainty

Answer 22

To find the absolute uncertainty in a calculated value for ab or a/b:

1. Find the percentage uncertainty in a and b.
2. Add the percentage uncertainties of a and b to find the percentage uncertainty in the calculated value.
3. Convert this percentage uncertainty to an absolute value.

Question 23

Fractional uncertainty

Answer 23

Fractional uncertainty =

absolute uncertainty/measured value

Question 24

Percentage error

Answer 24

The difference between the accepted and experimental value, expressed as a percentage of the accepted value.
Percentage error =
((accepted value-experimental value)/accepted value) * 100%

Question 25

Accepted value

Answer 25

literature value

Question 26

Propagation of error

Answer 26

Uncertainties in raw data lead to uncertainties in processed data. Propagation should be done in a consistent way.

Question 27

Adding and subtracting measurements

Answer 27

When adding or subtracting measurements, the uncertainty in the calculated value is the sum of the absolute uncertainties. The answer should be quoted to the same number of decimal places as the least precise value.

Question 28

Multiplying and dividing measurements

Answer 28

When multiplying or dividing measurements, the total percentage uncertainty is the sum of the individual percentage uncertainties. The answer should be quoted to the same number of significant figures as the least precise data.