topic eleven

Question 1

qualitative data

Answer 1

includes non-numerical data obtained from observations that are made during an experiment, not from actual measurements.

Question 2

quantative data

Answer 2

includes numerical data (numbers), such as measurements taken in the laboratory during an experiment. Examples include mass, volume, temperature, voltage, pH, density and absorbance. Remember that when recording a measurement, there is an experimental error or degree of random uncertainty associated with the value.

Question 3

SI units for electric current

Answer 3

amperes, A

Question 4

Si units for temperature

Answer 4

kelvin, K

Question 5

SI units frequency

Answer 5

hertz (reciprocal of seconds) Hz (s-1)

Question 6

SI units pressure

Answer 6

newtons per square metre Pa (Nm-2)

Question 7

examples of random errors

Answer 7

a breeze through an open door, which affects the mass measured on a mass balance

changes in the temperature of a room between morning and afternoon

errors of judgement when reading a scale on a measuring instrument.

Question 8

random erros cannot be eliminated completely, but they can be reduced by

Answer 8

conducting repeat trials and taking an average of to the results

Question 9

how to report measured quantities with a range of uncertainty

Answer 9

When taking a reading from analogue equipment (such as a measuring cylinder), you can estimate the value to within half of the smallest scale division. In the case of the measuring cylinder shown in Figure 1, the smallest scale division is 1 cm3, so half of the smallest division is 0.5 cm3.

Question 10

systematic errors are caused by

Answer 10

a piece of apparatus has been wrongly calibrated

a scale is consistently misread by the experimenter

the apparatus is faulty.

Question 11

examples of systematic errors include

Answer 11

not zeroing a mass balance before use (a non-zero error)

heat loss during an experiment to measure an enthalpy change

a leak in the apparatus used to measure a volume of gas.

Question 12

parallax error

Answer 12

when a scale or measuring cylinder is read from the wrong position

Question 13

systematic errors in determining enthalpay change

Answer 13

A significant proportion of the heat released by burning the alcohol is lost to the surroundings.

Heat is lost from the water and absorbed by the calorimeter itself.

Question 14

random errors when determining enthalpy change

Answer 14

Random uncertainties when recording the masses of the alcohol and the water.

Random uncertainties when recording the temperature of the water during the experiment.

Question 15

precision refers to

Answer 15

how close several experimental measurements or values are to each other

Question 16

accuracy refers to

Answer 16

how close the readings or values are to the actual value

Question 17

absolute uncertainity

Answer 17

The degree of uncertainty in a measurement is usually expressed in the same units as the measurement itself. This is the absolute uncertainty of the measurement, for example, 28.5 ± 0.1 °C

Question 18

in order to calculate the total uncertainty

Answer 18

the absolute uncertainties can either be added together or converted to percentage uncertainties, which are then added together.

Question 19

The equation used to calculate the percentage uncertainty is shown below:

Answer 19

Percentage uncertainty =
absolute uncertainty/measured value×100%

Question 20

percentage error equation

Answer 20

Percentage error = (experimental value - theoretical value) / theoretical value × 100%

Question 21

when plotting experimental data, the ind and dep variable goes on which axis

Answer 21

the independent variable is plotted on the x-axis and the dependent variable is plotted on the y-axis

Question 22

When plotting a graph:

Answer 22

plot the independent variable on the x-axis and the dependent variable on the y-axis

label the axes and ensure your labels include the correct units

choose an appropriate scale for each axis

give your graph an appropriate title

draw a line of best fit (see below).

Question 23

line of best fit

Answer 23

the line will not necessarily pass through all of the points; instead, you should try to ensure that approximately half the data points lie above the line, and half lie below. Outliers (points that do not seem to fit the overall trend) are not included in the data used to draw the line of best fit.

Question 24

gradient at a particular point on a curve

Answer 24

interpolation, draw a tangent to the curve at that point and find the gradient of the tangent using the relationship, m=change in y / change in x

Question 25

extrapolation on a graph

Answer 25

drawing the line further than where it goes
to find a data point outside the range of measured values.

Question 26

ihd formula

Answer 26

IHD=(2x + 2 - y)/2

Question 27

whicha toms dont affect the IHD

Answer 27

oxygen and sulfur

Question 28

what are halogen atoms treated as in ihd

Answer 28

hydrogen atoms

Question 29

what to do with nitrogen atoms in ihd

Answer 29

add one carbon and one hydrogen

Question 30

what is IR spectroscopy used for

Answer 30

to identify the bonds present within a molecule

Question 31

how is IR radiation use din IR spec

Answer 31

it is absorbed by certain types of bond and causes them to stretch or bend which can then be used to gain info about the type of bonds within the molecule

Question 32

Gases that absorb IR radiation are known as being

Answer 32

IR active

Question 33

amount of IR absorbed relies on

Answer 33

The amount of IR radiation absorbed by a bond depends on its polarity - strongly polar bonds absorb more and weakly polar bonds absorb less. Non-polar bonds such as C-C, for example, usually do not absorb IR radiation and do not show up on an IR spectrum.

Question 34

can divide IR into

Answer 34

functional group and fingerprint region

Question 35

wavenumber is equal to

Answer 35

the number of wavelengths per centimetre

Question 36

what do peaks correspond to

Answer 36

the amount of IR radiation absorbed by the bodns in the compound

Question 37

what is ionisation

Answer 37

where the sample in question is bombarded by high-energy electrons

Question 38

The collisions that take place in a mass spectrometer are so energetic that they cause the molecules to break up into different

Answer 38

fragments

Question 39

The fragmentation pattern produced in a mass spectrometer gives evidence about the

Answer 39

structure of the compound

Question 40

what can proton nmr identify

Answer 40

the different chemical environments in a molecule that contain hydrogen atoms (or protons).

Question 41

a higher-energy spin state (–½), when the nuclei line up with

Answer 41

their magnetic fields against the external magnetic field

Question 42

a lower-energy spin state (+½), when the nuclei line up with

Answer 42

their magnetic fields in the same direction as the external magnetic field.

Question 43

number of peaks in nmr gives

Answer 43

number of different chemical environments in which hydrogen atoms or protons are located

Question 44

in nmr, The position on the x-axis where a peak occurs is known as its

Answer 44

chemical shift, measured in ppm

Question 45

The chemical shift of each signal is measured relative to the peak produced by

Answer 45

tetramethylsilane (TMS)

Question 46

protons in the same chemical environment are known as

Answer 46

equivalen tprotons

Question 47

integrated trace

Answer 47

the height of each step is proportional to the number of protons in that chemical environment