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2 years ago

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A buffer is prepared by adding 100 mL of 0.50 M sodium hydroxide to 100 mL of 0.75 M propanoic acid. Is this a buffer solution,

and if so, what is its pH?

1 answer:

Yanka [14]2 years ago

7 0

The answer: is yes, It is a buffer solution.

first, we need to get moles of sodium hydroxide and propanoic acid:

moles NaOH = molarity * volume

= 0.5M * 0.1 L = 0.05 moles

moles propanoic acid = molarity * volume

= 0.75 M * 0.1 L = 0.075 moles

[NaOH] at equilibrium = 0.05 m

[propanoic acid ] at equilibrium = 0.075 - 0.05 = 0.025 m

when Pka for propanoic acid (given) = 4.89

so by substitution:

∴PH = Pka + ㏒[NaOH]/[propanoic acid ]

∴ PH = 4.89 + ㏒ 0.05 / 0.025

= 5.19

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The mass unit associated with density is usually grams. if the volume (in ml or cm3) is multiplied by the density (g/ml or g/cm3

jok3333 [9.3K]

The weight in grams = 7.93 g

Given volume = 2.00 $in^{3}$

Given density = 0.242 g/ $cm^{3}$

We need to find the Mass(weight) in grams.

To find the weight in grams we need to keep in mind that the volume and density must use the same volume unit for cancellation. So that the volume units will cancel out, leaving only the mass units.

The unit of given volume is $in^{3}$ and unit of volume in density is $cm^{3}$ , so first we need to change the unit of volume from $in^{3}$ to $cm^{3}$ so that the volume units will cancel out, leaving only the mass units.

1 $in^{3}$ = 16.39 $cm^{3}$ (given conversion)

$2 in^{3}\times \frac{(16.39 cm^{3})}{(1 in^{3})}$

$in^{3}$ units get cancel out leaving the $cm^{3}$ unit.

$2 in^{3} = 32.78 cm^{3}$

Mass = Density X Volume.

Density = 0.242 g/ $cm^{3}$ and Volume = 32.78 $cm^{3}$

$Mass =0.242\frac{g}{cm^{3}}\times 32.78 cm^{3}$

Mass = 7.93 grams (g)

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1 year ago

An atom of lead has a radius of and the average orbital speed of the electrons in it is about . Calculate the least possible unc

victus00 [196]

The question is incomplete. Here is the complete question.

An atom of lead has a radius of 154 pm and the average orbitalspeed of the electron in it is about 1.8x $10^{8}$ m/s. Calculate the least possible uncertainty in a measurement of the speed of an electron in an atom of lead. Write your answer as a percentage of the average speed, and round it to significant 2 digits.

Answer: v% = 0.21 m/s

Explanation: To calculate the uncertainty, use <u>Heisenberg's Uncertainty Principle</u>, which states that: ΔpΔx≥ $\frac{h}{4\pi }$

where h is <u>Planck's constant</u> and it is equal to 6.626. $10^{-34}$ m²kg/s.

Since p (momentum) is p = m.v:

mΔv.Δx ≥ $\frac{h}{4\pi }$

Δv = $\frac{h}{4\pi.x.m }$

Given that: r = x = 1.54. $10^{-10}$ m and mass of an electron is m=9.1. $10^{-31}$ kg

Δv = $\frac{6.626.10^{-34} }{4.3.14.1.54.10^{-10}.9.1.10^{-31}}$

Δv = 0.0376. $10^{7}$

As percentage of average speed:

Δv. $\frac{1}{v}$ .100% = $\frac{0.0376.10^{7} }{1.8.10^{8} }$ .10² = 0.021.10 = 0.21%

The least possible uncertainty in a speed of an electron is 0.21%.

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2 years ago

A metal rod with a length of 4.66 cm was measured using four different devices. Which of the following measurements is the most

iogann1982 [59]

4.658. Accuracy refers to how close the experimental value is to the actual value. Precision is how close a set of data is to one another.

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2 years ago

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Consider the reaction below. 2Al2O3 4Al + 3O2 How many moles of oxygen are produced when 26.5 mol of aluminum oxide are decompos

Aloiza [94]

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<u>calculation</u>

<u> </u> 2Al2O3 + 4Al +3 O2

use the mole ratio of Al2O3 to O2 to determine the moles of O2.

that is from the equation above the mole ratio of Al2O3 : O2 is 2:3

the moles of O2 is therefore=n 26.5 mol x3/2= 39.8 moles

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2 years ago

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A 0.133 mol sample of gas in a 525 ml container has a pressure of 312 torr. The temperature of the gas is ________ °c.

Serggg [28]

Answer:

$-253.2 ^{\circ}C$

Explanation:

First of all, we need to convert the pressure of the gas from torr to Pa. We know that:

1 torr = 133.3 Pa

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$p=(312 torr)(133.3 Pa/torr)=4.16\cdot 10^4 Pa$

Then we also have:

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$pV=nRT$

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In Celsius, it becomes

$T=19.8 K-273=-253.2 ^{\circ}C$

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1 year ago