Chemistry, 28.10.2020 16:50 emilylol04173

A chemistry graduate student is given of a hydrocyanic acid solution. Hydrocyanic acid is a weak acid with . What mass of should the student dissolve in the solution to turn it into a buffer with pH

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Answer from: raulflores01

Here is the full question:

A chemistry graduate student was given 500 mL of a 1.60 M hydrocyanic acid (HCN) solution. Hydrocyanic acid is a weak acid with $K_a = 4.9 \times 10^{-10}$ . What mass of KCN should the student dissolve in the HCN solution to turn it into a buffer with pH = 9.16?

36.85 g

Explanation:

From the given information above:

Recall that number of moles of HCN = mass of HCN / molar mass of HCN= mass of HCN / molar mass of HCN

Therefore;

the number of moles of HCN = $\dfrac{500 \times 1.60}{1000}$

the number of moles of HCN = $\dfrac{800}{1000}$

the number of moles of HCN = 0.8

The acid dissociation constant K_a = $4.9 \times 10^{-10}$

Thus the pKa = $- log (4.9 \times 10^{-10})$

pKa = 9.31

However, the pH is given as:

$pH = pKa + log \bigg ( \dfrac{KCN}{HCN} \bigg )$

$9,16 =9.31 + log \bigg ( \dfrac{KCN}{0.8} \bigg )$

$9,16 -9.31 =log \bigg ( \dfrac{KCN}{0.8} \bigg )$

$-0.15 =log \bigg ( \dfrac{KCN}{0.8} \bigg )$

KCN = 0.566 mol

The standard molar mass of KCN = 65.11 g/mol

Thus, the mass of KCN = number of moles of KCN × molar mass of KCN

the mass of KCN = 0.566 × 65.11

the mass of KCN that the student needs to dissolve in HCN is = 36.85 g

Answer from: Quest

most historians agree that gabriel mouton, the vicar of st. paul’s church in lyons, france, is the “founding father” of the metric system. he proposed a decimal system of measurement in 1670. mouton based it on the length of one minute of arc of a great circle of the earth (now called a nautical mile, 1852 meters). he also proposed the swing-length of a pendulum with a frequency of one beat per second as the unit of length (about 25 cm). a pendulum beating with this length would have been fairly easy to produce, thus facilitating the widespread distribution of uniform standards. over the years, his work was revised, improved, and extended by a number of french scientists.

the political sponsor of weights and measures reform in the french revolutionary national assembly was the bishop of autun, better known as talleyrand. under his auspices, the french academy appointed several committees to carry out the work of developing a usable system of weights and measures for france. one of the committees recommended a decimalized measurement system based upon a length equal to one ten-millionth of the length of a quadrant of the earth’s meridian (i.e., one ten-millionth of the distance between the equator and the north pole).

Answer from: Quest

Pcl5 + 4 h2o = h3po4 + 5 hclthe ratio is 1: 5 for pcl and hcl, 1 mole of pcl produces 5 moles of hclmolecular weight of pcl5 is: 31 + (5 x 35.5) = 208.5above we have 75.5 / 208.5 = 0.36 moles so this will produce0.36 x 5 = 1.81 moles of hcl.

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A chemistry graduate student is given of a hydrocyanic acid solution. Hydrocyanic acid is a weak aci...

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