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c5 Flashcards

(54 cards)

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1
Q

What does concentration mean

A

the amount or mass of a substance in a given volume of solution

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2
Q

Whats units of concentration

A

mol/dm^3
g/dm^3

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3
Q

How can concentration be calculated

A

moles/ volume(dm^3)
or mass / volume(dm^3)

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4
Q

How could you increase the concentration of a solution of hydrochloric acid

A

increase the number of moles of hydrochloric acid
or
decrease the volume of the solution

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5
Q

What equipment is required for a standard titration

A

burette
conical flask
pipette and pipette filler
white tile
funnel
clamp and stand

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6
Q

Describe how to carry out a standard acid/alkali titration to find the concentration of the alkali

A

add acid to burette. use pipette to add 25cm^3 of alkali to a conical flask.

add a few drops of indicator(methyl orange or phenolphthalein) to the conical flask

record initial burette reading. slowly add acid to conical flask, swirling constantly.

when the solution changes colour, stop adding the acid, and record final volume in the burette.

calculate the total volume of acid added from the burette.

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7
Q

why must the conical flask be swirled during a titration

A

to ensure all particles react

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8
Q

why is a white tile used when carrying out a titration

A

the white tile is placed under the conical flask so that the colour change of the indicator is easier to see.

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9
Q

after an acid/alkali titration, how can you calculate the concentration of the alkali if you know the concentration of the acid

A

multiply the concentration of acid by the volume from the burette to calculate number of moles of acid.

use balanced equation to get molar ratio of acid:alkali, then calculate number of moles of alkali from that.

then divide number of moles of alkali by initial volume of alkali in the conical flask

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10
Q

what is cm^3 dm^3 conversion rate

A

/1000

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11
Q

define the molar volume of a gas

A

the volume occupied by one mole of any gas at room temperature and pressure,

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12
Q

what is the molar volume of gas at room temperature and pressure

A

24dm^3 or 24000cm^3

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13
Q

what is rtp

A

room temperature and pressure:
20 degrees
1 atmosphere

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14
Q

how can the volume of gas be calculated at rtp

A

volume at rtp = moles x 24

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15
Q

why can the theoretical mass of a product be calculated if you know thee masses of all the other reactants and products

A

the law of conservation of mass means that the total mass of the reactants must equal the total mass of the products.

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16
Q

how can theoretical mass of a product be calculated using the mass of one reactant only.

A

divide the mass of the reactant by its molecular mass to find the number of moles.

work out the molar ratio of reactant to product and use this to find number of moles of thee product.

multiply the moles by molecular mass to find theoretical mass

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17
Q

how can percentage yield be calculated

A

(actual mass of product / theoretical mass of product) x100

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18
Q

Why is percentage yield usually less than 100%

A

incomplete reaction
some of the product may have escaped
impurities in the starting material

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19
Q

what is meant by atom economy

A

the proportion of reactant atoms which form the desired product in a reaction

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20
Q

what is formula for atom economy

A

(mr of desired product / total mr of reactants) x100

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21
Q

what is considered when choosing reaction pathway

A

percentage yield
atom economy
uses of by-products
rate of reaction
position of equilibrium
availability of reactants

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22
Q

how can rate of reaction be calculated

Study These Flashcards
A

amount of product formed or reactant used / time(s)

23
Q

give units that could be used for rate of reaction

Study These Flashcards
A

g/s
cm^3/s
mol/s

24
Q

how can rate of reaction be measured if a precipitate is produced

Study These Flashcards
A

place a conical flask over a black cross
start the timer as soon as the reactants are combined in the conical flask
time how long it takes for the black cross to disappear

25
why is the disappearing cross rate of reaction experiment not very accurate
its subjective as people may disagree about the exact point when the cross disappears
26
how can the rate of reaction bee measured if hydrogen is produced
by collecting gas in a gas syringe or upturned measuring cylinder in a water trough. Reactants are placed in a conical flask with a bung and delivery tube with connects to where gas is collected. timer for 30 seconds. use volume of gas collected and the timer to calculate rate of reaction
27
when and how can the rate of reaction be measured using a digital mass balance.
when a gas is produced, as gas will escape so mass decreases. record initial mass of reactants. start timer when they combine record mass every 15 seconds for 2 minutes calculate rate of reaction
28
how could you investigate the effect of temperature on the rate of reaction
calculate rate of reaction then repeat the experiment at different temperatures and then plot them on a graph to compare them
29
how can rate of reaction be calculated at a specific time in a reaction
plot the rate of reaction results onto a graph and draw a tangent at the specific time, then rate of reaction at that time is equal to gradient of the tangent.
30
how does concentration of reactants and products change during a reaction
the concentrations of products increase rapidly at the start then slows down before staying constant when the reaction is complete. the concentrations of the reactants decrease as the reaction progresses. They decrease rapidly at the start then slow down before staying constant when one or all of the reactants have been used up.
31
describe and explain the gradient of the curve on a rate of reaction graph.
initially the gradient is very steep because the rate of reaction is fastest at the start.(more reacting particles so more frequent successful collisions) The gradient decreases over time as the reactants are used up. the curve eventually levels off when the reaction is complete.
32
what is proportional to the rate and gradient of a rate of reaction graph.
1/t
33
what does activation energy mean
the minimum amount of energy required for a reaction to take place
34
what conditions can be changed to increase the rate of reaction
increase temperature increase pressure increase surface area of reactants increase concentration of reactants
35
how does temperature affect rate of reaction
increasing temperature increases the rate of reaction because higher temperature means the particles have more kinetic energy, meaning they move quicker so collisions are more frequent. Collisions are also more likely to be successful as more reactant particles have energy above the activation energy
36
how does surface area affect the rate of reaction
increasing surface area increases the rate of reaction because more reacting particles are exposed so there are more frequent successful collisions
37
how does concentration affect the rate of reaction
increasing concentration increases the rate of reaction because there are more reacting particles in the same volume. This means more frequent successful collisions occur.
38
how does pressure affect the rate of a gaseous reaction
increasing the pressure of a gaseous reaction increases the rate of reaction because there are more reacting particles in the same volume of gas so there are more frequent successful collisions.
39
how can you increase the rate of reaction of this reaction: marble chips + hydrochloric acid --> calcium chloride + water + carbon dioxide
increase surface area of marble chips by turning them into powder increase concentration of acid increase temperature of reaction
40
how can a catalyst be identified in a reaction
they are chemically unchanged so can be distinguished from the product. They are not involved in the reaction equation as they are not used up
41
what is a catalyst
a substance which speeds up the rate of reaction without being chemically changed at the end.
41
what can be added to speed up rate of a reaction
a catalyst
42
how does a catalyst affect the rate of reaction
it increases the rate of reaction because it provides an alternate reaction pathway with a lower activation energy. More particles have energy above the activation energy so more frequent successful collisions will occur.
43
what does exothermic mean
a reaction that gives out energy to the surroundings
44
what are enzymes
biological catalysts that speed up the rate of reactions in living cells.
44
what does endothermic mean
a reaction that takes in energy from the surroundings
45
what is a reversible reaction
a reaction in which the products can react together to reform the original reactants
46
how can the direction of a reversible reaction be changed
by changing the conditions
47
what is meant by the term dynamic equilibrium
dynamic equilibrium occurs in a closed system when the rates of the forward and backward reactions are equal. The concentration of reactants and products remain constant
48
What is Le Chatelier's principle
If a reaction at equilibrium is subjected to a change in temperature, concentration or pressure, the position of equilibrium will shift to oppose this change
49
what happens to the position of equilibrium if the concertation of the products increases
it will shift left(towards the reactants) to decrease the concentrations of products and form more reactants.
49
what happens to the position of equilibrium if the concentration of the reactants increases
it will shift right(towards the products) to reduce the concentration of reactants and form more products
50
how does a change in pressure affect the position of equilibrium
increasing the pressure causes the position of equilibrium to shift towards the side with the fewest gaseous moles in order to counteract the pressure change
51
What happens to the position of equilibrium if the temperature of a reaction is increased?
it shifts in the direction of the endothermic reaction, to take in more heat energy form the surroundings
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