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cestrela7 [59]
3 years ago
9

The half-life of a strontium isotope is 25 years. How much of this particular isotope will remain after 100 years if the startin

g mass is 16 grams?
Chemistry
1 answer:
Phoenix [80]3 years ago
3 0

Answer:

1 gram

Explanation:

Half life = 25 years

Starting mass = 16 grams

Time = 100 years

Number of half lives = Time / Duration of Half life = 100 / 25 = 4

After first Half life;

Remaining mass = 16 / 2 =  8 g

After Second Half life;

Remaining mass = 8 / 2 =  4 g

After Third Half life;

Remaining mass = 4 / 2 =  2 g

After Fourth Half life;

Remaining mass = 2 / 2 = 1 g

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A sodium hydroxide solution is made by mixing 8.70 g NaOH with 100 g of water. The resulting solution has a density of 1.087 g/m
Ahat [919]

Answer:

Mass fraction = 0.08004

Mole fraction = 0.0377

Explanation:

Given, Mass of NaOH = 8.70 g

Mass of solution = 8.70 + 100 g = 108.70 g

Mass\ fraction\ of\ NaOH=\frac {8.70}{108.70} = 0.08004

Molar mass of NaOH = 39.997 g/mol

The formula for the calculation of moles is shown below:

moles = \frac{Mass\ taken}{Molar\ mass}

Thus,

Moles= \frac{8.70\ g}{39.997\ g/mol}

Moles\ of\ NaOH= 0.2175\ mol

Given, Mass of water = 100 g

Molar mass of water = 18.0153 g/mol

The formula for the calculation of moles is shown below:

moles = \frac{Mass\ taken}{Molar\ mass}

Thus,

Moles= \frac{100\ g}{18.0153\ g/mol}

Moles\ of\ water= 5.5508\ mol

So, according to definition of mole fraction:

Mole\ fraction\ of\ NaOH=\frac {n_{NaOH}}{n_{NaOH}+n_{water}}

Mole\ fraction\ of\ NaOH=\frac {0.2175}{0.2175+5.5508}=0.0377

3 0
3 years ago
Which of the following compounds' solubility will not be affected by a low pH in solution?
Whitepunk [10]

The compound solubility which will not be affected by a low pH in solution is AgBr.

<h3>What is pH?</h3>

pH is a measure of the acidity or basicity of any solution and according to the pH scale 0 to 6.9 shows the acidity, 7 is neutral and 7.1 to 14 shows the basicity of any solution.

  • AgBr is sparingly soluble in water and not soluble in acids, so if we low the pH of the solution towards the acidity its solubility not affected.
  • NiCO₃ is a basic salt and and shows solubility in the acidic medium so change in pH will affect its solubility.
  • Co(OH)₂ it is also a basic compound and shows its solubility in the acidic medium and get affected when change in pH takes place.
  • PbF₂ is a strong base and also shows solubility in the acidic medium easily, so get affected when change in pH takes place.
  • In CuS, sulphide is basic ion and whole compound shows solubility in the acidic medium and get affected when low pH of solution takes place.

AgBr is not affected by a low pH in solution.

To know more about solubility, visit the below link:

brainly.com/question/23946616

3 0
2 years ago
Read 2 more answers
What’s the answer for #9
zheka24 [161]
Freezer and refrigerator--> Too cold for most bacteria to grow (reproduce). Oven --> too hot for bacteria to survive
4 0
3 years ago
Medicine and urine are seperated by which method?​
vovikov84 [41]

Answer:

Screening for the presence of drugs in serum and urine using different separation modes of capillary electrophoresis. The most common mode is capillary zone electrophoresis (CZE), in which charged analytes migrate in a buffer under the influence of an electric field.

Explanation:

7 0
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.
AlekseyPX

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

5 0
3 years ago
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