8/10/2019 Calculations LBL2
1/8
1. Define the following:
a) mass,
b) volume,
c) amount,d) concentration,
e) dilution.
Give examples of typical units used to describe each of the above.
Answer:
he units of measurement in current use are those of the !ysteme "nternational
d#$nites %!"), 1&'(.
a) ass can be defined as a measure of how much matter is in an ob*ect. ass ismeasured in +ilogrammes %+g).
b) A measurement of the amount of space contained within a threedimensional
shape. -olumes in the laboratory are measured in litres or parts of a litre litre
is not an !" $nit but a metric unit. he !" unit for volume is cubic metres
%m/).
c) he amount of a substance that contains as many elementary units as there are
atoms in (.(10 +g of carbon10. he !" unit for amount of substance is moles
%mol).
d) he concentration of a solution is expressed as the amount of solute in a given
volume of liuid
2oncentration 3 4umber of moles
-olume of solvent %5)
3 mol65
7e can express concentration as mass per volume e.g. 0( grams6 litre. 7e can
also express concentration in terms of moles per litre. here are three different
ways of writing this, either (.1 moles6litre or (.1 mol51 or (.1. he 8#stands for molar.
e) 9rocess of reducing the concentration of a solute in solution, usually simply by
mixing with more solvent.
ou can calculate the concentration of a solution following a dilution by
applying this euation:
i-i 3 f-f
7here is molarity, - is volume, and the subscripts i and f refer to the initial
and final values.
Atif !hah;ad 711
8/10/2019 Calculations LBL2
2/8
=xample:
>ow many millilitres of ?.? 4a@> are needed to prepare /(( m5 of 1.0
4a@>
!olution:
?.? x -1 3 1.0 x (./ 5-1 3 1.0 x (./ 5 6 ?.?
-1 3 (.('? 5
-1 3 '? m5
!o, to prepare the 1.0 4a@> solution, you pour '? m5 of ?.? 4a@> into
your container and add water to get /(( m5 final volume.
0. 4ame and define the correct !" unit for each of the following:
a) amount,
b) volume,c) time,
d) en;yme activity.
Answer:
a) he !" unit for amount of substance is moles %mol). A mole is defined as the
amount of substance that contains as many elementary particles %atoms, ions,
molecules) as there are in 10g of carbon10 atoms.
b) he !" unit for volume is cubic metres %m/). "t is defined as a volume that is
made by a cube that is 1 meter on each side. "t is eual to 1((( %one thousand)
litres.
c) he second is the basic unit of time. he time ta+en for &,1&0,'/1,BB( periods
of vibration of the caesium1//atom to occur.
d) he !" unit is the +atal and is used to measure total units of activity in a given
volume of solution.
1 +atal 3 1 mol sC1
atal, however is an excessively large unit. A more practical and commonlyused value is 1 en;yme unit %$) 3 1 Emol minC1. 1 $ corresponds to
1'.'B nano+atals.
/. 7riting the answers in both decimal form and in standard form:
a) =xpress F.< mmol as %i) mol %ii) nmol and %iii) mol
b) =xpress 0B.' 5 as %i) m5 and %ii) li tres
Answer:
a) F.< mmol
Atif !hah;ad 711
8/10/2019 Calculations LBL2
3/8
i) F.
8/10/2019 Calculations LBL2
4/8
c) Ieporting your answer to / significant figures, what will the final
concentration of urea be if 1.0? m5 of stoc+ solution is mixed with
0.?( m5 water
Answers:
a)
2oncentration ( mmol65 ? mmol65 1?
mmol65
0(
mmol65
/?
mmol65
-olume of stoc+
standard %m5)
( (.? 1.? 0 /.?
-olume of water
%m5)
?
8/10/2019 Calculations LBL2
5/8
$sing the euation
i-i3f-f
?(mmol65 x 1.0?m5 3 f x 0.?( m5
f3 ?(mmol65 x 1.0?m560.?(m5f3 0?mmol65
Jinal concentration of urea 3 0?mmol65 or 0?( x 1(H1 mmol65
?. 2onvert (.0F0? g65 creatinine solution to molar, millimolar and
micromolar concentrations. %creatinine has the molecular formula
2B4/@)
Answer:
olar ass of 2reatinine3 11/.10
Amount %in moles) 3 Amount %in g) 6 olar ass %g.mol1)
3 (.0F0?g 6 11/.10 g.mol1
3 (.((0? mol
2oncentration %) 3 Amount %in mol) 6 -olume %in 5)
3 (.((0?mol615
2oncentration %) 3 (.((0?
@r in millimolar
2oncentration %) 3 (.((0? x 1(H/m6
3 0.?m
or in micromolar
2oncentration %) 3 (.((0? x 1(H'6
3 0?(( or 0.? x 1(H/
'. A urine sample that has tested positive for blood using a dipstic+
reuires red and white blood cell counts to be underta+en. he number
of cells is counted in a three separate haemocytometer grids of
dimensions 1 mm x (.0 mm x (.< mm. 2alculate the number of red and
white blood cells per microlitre, per millilitre and per litre of the patient
sample from the following grid counts.
a) Ied blood cell counts: 0/, 1&, 0?b) 7hite blood cell counts: F, &, 11
Atif !hah;ad 711
8/10/2019 Calculations LBL2
6/8
Answer:
a) Ied 2ell 2ounts
i. 2alculate average of the counts %0/K1&K0?)6/ 3 00.//ii. he volume of the suare of the counting chamber in which the cells
were counted is 1x(.0x(.
8/10/2019 Calculations LBL2
7/8
a) 7hat data is missing from the above
b) 7hat limits the usefulness of the information above
c) 9lot a line graph to represent the above data using icrosoft =xcel,
ensure full labelling.
d) 9lot a bar chart of the mean number of samples from each G9 surgeryusing icrosoft =xcel.
Answer:
a) 7hat data is missing from the above
here is no data regarding number of staff during the laboratory wor+ing
hours.
b) 7hat limits the usefulness of the information above
Mecause there is no data regarding staffing levels in the laboratory during its
wor+ing hours, the above data limits its usefulness to address the pea+ times in
the laboratory.
c) 9lot a line graph to represent the above data using icrosoft =xcel, ensure full
labelling.
d) 9lot a bar chart of the mean number of samples from each G9 surgery using
icrosoft =xcel.
Atif !hah;ad 711
8/10/2019 Calculations LBL2
8/8
Atif !hah;ad 711
Top Related