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3 years ago

A substance which melts/boils at a fixed temperature is a pure substance. True False

Chemistry

2 answers:

ololo11 [35]3 years ago

3 0

True

when a substance is impure, it boils over a range of temperature rather than a specific temperature

ASHA 777 [7]3 years ago

3 0

I believe the correct answer is true. <span>A substance which melts/boils at a fixed temperature is a pure substance. This is because the substance is homogeneous throughout that the properties as well would be uniform. Hope this answers the question. Have a nice day.</span>

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How many molecules are in 3.40 mol He?

shutvik [7]

Answer:

20.5 × 10²³ molecules of He

Explanation:

Given data:

Number of moles of He = 3.40 mol

Number of molecules of He = ?

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 molecules of water

1.008 g of hydrogen = 1 mole = 6.022 × 10²³ atoms of hydrogen

For 3.40 moles of He:

3.40 mol × 6.022 × 10²³ molecules

20.5 × 10²³ molecules of He

8 0

4 years ago

Assuming that the F−18 can be transported at 59.0 miles/hour, how close must the hospital be to the cyclotron if 68% of the F−18

tekilochka [14]

Answer:

60.12 miles

Explanation:

Using the calculation formula shown below:

$t_{1/2} =\frac{t}{[tex]log_{2}$ \frac{N_{o} }{N_{t} } }[/tex]

where:

$t_{1/2}$ is the half life, $N_{o}$ is the original amount of F-18, and $N_{t}$ is the remaining amount of F-18 at time t.

Generally, F-18 has an half life of 1.83 hours.

Therefore:

$t = 1.83*[tex]log_{2}$ \frac{100}{68} = 1.02 hours[/tex]

Therefore using a speed of 59 miles/hour, the closeness of the hospital is:

distance = speed*time = 59*1.02 = 60.12 miles

6 0

3 years ago

If a swimming pool contains 2,850 kiloliters (kL) of water, how many gallons (gal) of water does it contain? (1 gal = 3.785 L)

siniylev [52]

we are given

a swimming pool contains 2,850 kiloliters (kL) of water

2,850 kiloliters (kL)=2850000L

we know that

$1gal=3.785L$

$3.785L=1gal$

Firstly , we will find for 1L

$1L=\frac{1}{3.785}gal$

now, we can multiply both sides by 2850000

$2850000*1L=2850000*\frac{1}{3.785}gal$

$2850000L=2850000*\frac{1}{3.785}gal$

$2850000L=752972.25892gal$

so,

a swimming pool contains 752972.25892gal of water...........Answer

6 0

4 years ago

Read 2 more answers

Good and bad effects of changes in materials in the environment

Sholpan [36]

Answer:

Composting, recycling, technological development, water cycle and photosynthesis are changes that have good effects. Some changes have bad effect like pollution and destruction of habitat and lose of lives.

Explanation:

hope it helps

8 0

3 years ago

When of glycine are dissolved in of a certain mystery liquid , the freezing point of the solution is lower than the freezing poi

Nesterboy [21]

The given question is incomplete. The complete question is:

When 282. g of glycine (C2H5NO2) are dissolved in 950. g of a certain mystery liquid X, the freezing point of the solution is 8.2C lower than the freezing point of pure X. On the other hand, when 282. g of ammonium chloride are dissolved in the same mass of X, the freezing point of the solution is 20.0C lower than the freezing point of pure X. Calculate the van't Hoff factor for ammonium chloride in X.

Answer: the van't Hoff factor for ammonium chloride is 1.74

Explanation:

Depression in freezing point is given by:

$\Delta T_f=i\times K_f\times m$