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ESAT Chemistry and Biology Key Facts

30 flashcards on quantitative chemistry, periodic trends, redox, rates, energetics, cells, genetics, enzymes, physiology and ecology for ESAT Chemistry and Biology. Original study material for practice.

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Moles from mass, volume of solution and gas volume

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Moles from mass, volume of solution and gas volume

n = \frac{m}{M}

n = c V

(with

V

in dm

^{3}

) and

n = \frac{V}{24}

for a gas at RTP (V in dm

^{3}

Percentage yield and atom economy

Yield

= \frac{actual}{theoretical} \times 100

; atom economy

= \frac{M _{r} of desired product}{total M _{r} of products} \times 100

Empirical formula method

Divide each percentage (or mass) by

A_{r}

to get moles, divide by the smallest, then scale to whole numbers.

Relative atomic mass from isotopes

The abundance-weighted mean of the isotope mass numbers.

Trend in reactivity down Group 1 and why

Reactivity increases because the outer electron is further from the nucleus and more shielded, so it is lost more easily.

Trend in reactivity down Group 7 and displacement

Reactivity decreases down the group; a more reactive halogen displaces a less reactive halide from solution.

Flame test colours

Lithium crimson, sodium yellow, potassium lilac, calcium orange-red, copper blue-green.

Silver nitrate test for halides

Chloride gives a white precipitate, bromide cream, iodide yellow (acidify with nitric acid first).

Shapes of small molecules

CH_{4}

tetrahedral,

NH_{3}

trigonal pyramidal,

H_{2} O

bent,

CO_{2}

linear.

Why graphite conducts but diamond does not

Graphite has one delocalised electron per carbon between its layers; in diamond all four outer electrons are in covalent bonds.

Oxidation and reduction

OIL RIG: oxidation is loss of electrons (oxidation number increases); reduction is gain (oxidation number decreases).

Disproportionation

One species is both oxidised and reduced in the same reaction, such as chlorine in cold alkali.

Five factors that change the rate of reaction

Temperature, concentration or pressure, surface area, a catalyst, and light for some reactions.

What a catalyst does

Provides an alternative pathway with a lower activation energy and is unchanged at the end.

Enthalpy change from a temperature rise

q = m c Δ T

, then

Δ H = \frac{- q}{n}

(negative for a temperature rise).

Enthalpy change from bond energies

Δ H =

energy to break bonds

-

energy released on making bonds.

pH and strong acids

pH = - lo g_{10} [H^{+}]

; a strong monoprotic acid of concentration

c

has

pH = - lo g_{10} c

Osmosis

Net movement of water across a partially permeable membrane from higher to lower water potential.

Mitosis compared with meiosis

Mitosis: one division, two identical diploid cells. Meiosis: two divisions, four genetically different haploid cells.

Semi-conservative replication

Each new DNA molecule contains one original strand and one newly synthesised strand.

Stages of PCR

Denature at about 95 degrees C, anneal primers at about 55 degrees C, extend with Taq polymerase at about 72 degrees C.

Gel electrophoresis of DNA

DNA is negatively charged and moves towards the positive electrode; shorter fragments travel further.

Enzyme specificity and inhibition

A competitive inhibitor binds the active site and is overcome by more substrate; a non-competitive inhibitor binds elsewhere and alters the active site.

Hardy-Weinberg equations

p + q = 1

and

p^{2} + 2 pq + q^{2} = 1

;

2 pq

is the frequency of heterozygotes.

Chi-squared test statistic

χ^{2} = \sum \frac{( O - E ) ^{2}}{E}

, compared with a critical value at the chosen significance level.

Cardiac output

Heart rate

\times

stroke volume.

Simpson's index of diversity

D = 1 - \frac{\sum n ( n - 1 )}{N ( N - 1 )}

Mark-release-recapture estimate

Population

= \frac{first sample marked \times second sample size}{marked in second sample}

Stages of the Calvin cycle

Rubisco fixes carbon dioxide onto RuBP to make GP; GP is reduced to triose phosphate using ATP and reduced NADP; some triose phosphate regenerates RuBP.

Cohesion-tension in the xylem

Transpiration lowers water potential in the leaf; cohesive water molecules are pulled up the xylem in a continuous column.

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