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3 years ago

What is the pH of a mixture of 0.042 M NaH2PO4 and 0.058 M Na2HPO4? Hint: The pKa of phosphate is 6.86.

Chemistry

1 answer:

AlekseyPX3 years ago

5 0

Answer:

The pH value of the mixture will be 7.00

Explanation:

Mono and disodium hydrogen phosphate mixture act as a buffer to maintain pH value around 7. Henderson–Hasselbalch equation is used to determine the pH value of a buffer mixture, which is mathematically expressed as,

$pH=pK_{a} + log(\frac{[Base]}{[Acid]})$

According to the given conditions, the equation will become as follow

$pH=pK_{a} + log(\frac{[Na_{2}HPO_{4} ]}{[NaH_{2}PO_{4}]})$

The base and acid are assigned by observing the pKa values of both the compounds; smaller value means more acidic. NaH₂PO₄ has a pKa value of 6.86, while Na₂HPO₄ has a pKa value of 12.32 (not given, but it's a constant). Another more easy way is to the count the acidic hydrogen in the molecular formula; the compound with more acidic hydrogens will be assigned acidic and vice versa.

Placing all the given data we obtain,

$pH=6.86 + log(\frac{0.058}{0.042})$

$pH=7.00$

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3 years ago

6. The Earth’s electric field is directed vertically downward; at the ground level its strength is E = 130 N/C, and at an altitu

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Answer:

5.31x10⁻⁶ C

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The cube is located 100 m altitude from the ground, so the superior face is at 100m and has E = 70 N/C, and the inferior face is at the ground with E = 130 N/C.

The electric field is perpendicular to the bottom and the top of the cube, so the total flux is the flux at the superior face plus the flux at the inferior face:

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Where Ф = E*A*cos(α). α is the angle between the area vector and the field (180° at the topo and 0° at the bottom):

Фtotal = E100*A*cos(180°) + Eground*A*cos(0°)

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By Gauss' Law, the flux is:

Фtotal = q/ε, where q is the charge, and ε is the permittivity constant in vacuum = 8.854x10⁻¹² C²/N.m²

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2 years ago

Classify methanal according to the position of the c=o group

seraphim [82]

Answer : Methanal also known as Formaldehyde $CH_{2}O$ is a chemical Aldehyde which contain ( -CHO) group.

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In organic chemistry, a carbonyl group is a functional group which contain a carbon atom double-bonded to an oxygen atom i.e, ( C=O).

If carbonyl group is present in a compound then it can be a carboxylic (RCOOH), aldehyde (RCHO), ketone (RCOR'), ester ((RCOOR') or amide (RCONR'R") group.

Here are some functional groups naming according to the<em> IUPAC</em> rules and image also attached,

Carboxylic acid → (RCOOH) → ( name end in 'OIC ACID' )

Aldehyde → (RCOH) → ( name end in 'AL' )

Ketone → (RCOR') → ( name end in 'ONE' )

Ester → (RCOOR') → ( name end in 'ATE' )

Amide → (RCONR'R") → ( name end in 'AMIDE' )

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Methanal is the IUPAC name for Formaldehyde.

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3 years ago