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3 years ago

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Chemistry

1 answer:

matrenka [14]3 years ago

6 0

Answer:

С. After evaporating a liquid, there is nothing left behind

Explanation:

In chemistry, a pure substance is that substance that has a definite chemical composition. It cannot be separated using physical means as the chemical bonds that forms it have to be broken. Pure substances include elements and compounds.

According to this question, a good evidence that an unknown sample is a pure substance would be that: After evaporating a liquid, there is nothing left behind. This means that after using physical separation technique, THE PURE SUBSTANCE COULD NOT BE SEPARATED, hence, nothing is left behind.

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An atom with an atomic number of 10 and a mass number of 24 would have ________.

Anastaziya [24]

An atom with an atomic number of 10 and a mass number of 24 would have 14 neutrons.

<h3>What is atomic number and mass number?</h3>

The term atomic number, conventionally denoted by the symbol Z.

Atomic number indicates the number of protons present in the nucleus of an atom, which is also equal to the number of electrons in an uncharged atom.

The mass number of a given atom is defined by the number of protons and neutrons present in the nucleus. In simple,

Protons + Neutrons = Mass Number

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2 years ago

If an object has more positive charges than negative charges, the object has an overall?

guapka [62]

It will have an overall positive charge.

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3 years ago

When a sodium (Na) atom forms an ion so that it looks like a noble gas with a full valence shell, what will its charge be?

Setler79 [48]

Answer:

I believe 1+

Explanation:

when Na loses 1 electron in the outer shell it has 8 valence protons on it's new most outer shell. so now it has 11 protons and 10 electrons. that extra proton (positively charged) adds one extra charge. so +1

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3 years ago

Find the enthalpy of neutralization of HCl and NaOH. 137 cm3 of 2.6 mol dm-3 hydrochloric acid was neutralized by 137 cm3 of 2.6

liraira [26]

Answer : The correct option is, (D) 89.39 KJ/mole

Explanation :

First we have to calculate the moles of HCl and NaOH.

$\text{Moles of HCl}=\text{Concentration of HCl}\times \text{Volume of solution}=2.6mole/L\times 0.137L=0.3562mole$

$\text{Moles of NaOH}=\text{Concentration of NaOH}\times \text{Volume of solution}=2.6mole/L\times 0.137L=0.3562mole$

The balanced chemical reaction will be,

$HCl+NaOH\rightarrow NaCl+H_2O$

From the balanced reaction we conclude that,

As, 1 mole of HCl neutralizes by 1 mole of NaOH

So, 0.3562 mole of HCl neutralizes by 0.3562 mole of NaOH

Thus, the number of neutralized moles = 0.3562 mole

Now we have to calculate the mass of water.

As we know that the density of water is 1 g/ml. So, the mass of water will be:

The volume of water = $137ml+137ml=274ml$

$\text{Mass of water}=\text{Density of water}\times \text{Volume of water}=1g/ml\times 274ml=274g$

Now we have to calculate the heat absorbed during the reaction.

$q=m\times c\times (T_{final}-T_{initial})$

where,

q = heat absorbed = ?

$c$ = specific heat of water = $4.18J/g^oC$

m = mass of water = 274 g

$T_{final}$ = final temperature of water = 325.8 K

$T_{initial}$ = initial temperature of metal = 298 K

Now put all the given values in the above formula, we get:

$q=274g\times 4.18J/g^oC\times (325.8-298)K$

$q=31839.896J=31.84KJ$

Thus, the heat released during the neutralization = -31.84 KJ

Now we have to calculate the enthalpy of neutralization.

$\Delta H=\frac{q}{n}$

where,

$\Delta H$ = enthalpy of neutralization = ?

q = heat released = -31.84 KJ

n = number of moles used in neutralization = 0.3562 mole

$\Delta H=\frac{-31.84KJ}{0.3562mole}=-89.39KJ/mole$

The negative sign indicate the heat released during the reaction.

Therefore, the enthalpy of neutralization is, 89.39 KJ/mole

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4 years ago

What is the main purpose of patent attorneys?

Aneli [31]

To protect the patents of those they work . Patents are legal rights of ownership to something that you have made or created.

Please vote my answer branliest! Thanks .

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3 years ago

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