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Ghella [55]
3 years ago
15

(25 points) A certain isotope of technetium has a half-life of 8 hours. How much of a 40 gram sample will be left after 16 hours

?
A. 10 grams
B. 40 grams
C. 5 grams
D. 20 grams
Chemistry
1 answer:
gtnhenbr [62]3 years ago
6 0

Answer:

A) 10 grams

Explanation:

16 hours = 2 half lives

This means that the number is divided in half twice.

40/2 = 20

20/2 = 10

I hope this helps!! :)

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3 years ago
how many moles of sodium hydroxide would have to be added to 250 ml of a 0.403 m acetic acid solution, in order to prepare a buf
jonny [76]

The volume of the buffer solution having a ph value is calculated by henderson's hasselbalch equation.

Buffer solution is water based solution which consists of a mixture containing a weak acid and a conjugate base of the weak acid. or a weak base and conjugate acid of a weak base.it is a mixture of weak acid and a base. The pH of the buffer solution is determined by the expression of the henderson hasselbalch equation.

              pH=pKa + log [salt]/[acid]

Where, pKa =dissociation constant , A- = concentration of the conjugate base, [HA]= concentration of the acid. Here, a buffer solution contains 0.403m acetic acid  and 250 ml is added  in order to prepare a buffer with a ph of 4.750. Putting all the values in the henderson hasselbalch equation we find the pH of the buffer solution.

To learn more about hendersons hasselbalch equation please visit:

brainly.com/question/13423434

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6 0
1 year ago
7. How many formula units are equal to a 0.25 g sample of Chromium (III) sulfate,
ryzh [129]

Answer:

38.541 × 10¹⁹ formula units

Explanation:

Given data:

Mass of chromium sulfate = 0.25 g

Formula units in 0.25 g = ?

Solution:

The given problem will solve by using Avogadro number.

It is the number of atoms , ions and molecules in one gram atom of element, one gram molecules of compound and one gram ions of a substance.

The number 6.022 × 10²³ is called Avogadro number.

For example,

18 g of water = 1 mole = 6.022 × 10²³ formula units of water

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Number of moles of chromium sulfate = 0.25 g/ 392.16 g/ mol

Number of moles of chromium sulfate = 6.4 × 10⁻⁴ moles

Number of formula units:

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6.4 × 10⁻⁴ moles × 6.022 × 10²³ formula units / 1 mol

38.541 × 10¹⁹ formula units

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kobusy [5.1K]
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A chemical element bonded to an identical chemical element is not a chemical compound since it is made from only one element and not from two different elements. Chlorine is molecule, but not compound.
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