Help for chemistry assignment

[popcornfrenzy]

 

How do you calculate the % water ? Let's say the % purity of Muriatic Acid is 18% how do you calculate the % Water?

In terms of the reason for difference what should I look at? Like the dissolution? IDK how I would compare these solutions as they have different uses and properties. 

[studiot]

9 hours ago, popcornfrenzy said:

How do you calculate the % water ? Let's say the % purity of Muriatic Acid is 18% how do you calculate the % Water?

In terms of the reason for difference what should I look at? Like the dissolution? IDK how I would compare these solutions as they have different uses and properties. 

Good morning.

What subject are you studying this in, and at what level ? Is it General Science or something at higher level ?

Muriatic acid is a very old name - in all the 60 years since I have known anything about it I have never seen the name used.

So I will try to address other older conventions in my reply as well.

 

The quantity of substances can be measured in several ways : weight, mass, volume (also called capacity) count (eg gram-moles) or pressure.

Since the substances may be in any of the three normal states of matter (solid, liquid or gas), or the dissolved state some measures are more convenient than others.

 

When you come to mixtures there is a comparison of more than one substance quantity and the units of measure can themselves be mixtures of the above listed measures.

Common measures are weight per volume (w/v) ; volume per volume (v/v) ; weight per weight (w/w) ; and moles per volume (mol/litre)

 

So you should look carefully at the labels for one of the above abbreviations on the labels you are told to read.

Without this information you cannot answer the question.

When it comes to percentages, unfortunately different industries use the % in different ways so my preamble is important.

Here are two different listings for 18% HCl  - one is w/w the other is v/v

Quote

 

Hydrochloric Acid, 18% (v/v), Ricca Chemical, Quantity: 10 L

www.fishersci.com › ... › Acids › Inorganic Acids › Hydrochloric Acid

Hydrochloric Acid, 18% (v/v), Ricca Chemical. SDP ; CAS Max %, 84.0, 17.87 ; Physical Form, Liquid ; Concentration or Composition (by Analyte or Components), 18% ( ...

CAS: 7647-01-0, 7732-18-5
Molecular Weight (g/mol): 36.46

 

 

Quote

 

Hydrochloric Acid, 18% (w/w) Volumetric - Reagents

www.reagents.com › Product › Hydrochloric-Acid-18-w-w-

US$258.10

Composition, : Water 81.75%, Hydrochloric Acid 18.25% ; Concentration, : 18% w/w ; DOT, : UN1789, HYDROCHLORIC ACID SOLUTION, 8, P.G. II ; Density, : 1.09 ; Melting ...

 

Either way the % is a fraction of the total amount  - which is the sum of the water and the HCl in a given mass or volume

 

Your 18 % Hydrochloric acid is a common cleaning concentration in engineering and often refers to what is called the mass fraction  - a w/w measure.

It means that of the total mass, 18% is HCl and the rest is water.

So M_w is the mass of water and M_HCl is the mass of HCl then

[math]\frac{{18}}{{100}} = \frac{{{M_w}}}{{{M_w} + {M_{HCl}}}}[/math]

or

[math]\frac{{18}}{{100}} = \frac{{{V_w}}}{{{V_w} + {V_{HCl}}}}[/math]

for the volume fraction

You should be able to solve this for the mass of water.

 

 

Does this help ?

 

 

 

 

 

Edited March 11, 2023 by studiot

[studiot]

OOPs I posted the wrong equation for the mass ratio.

 

[math]\frac{{18}}{{100}} = \frac{{{M_{HCl}}}}{{{M_{HCl}} + {M_w}}}\quad where\;{M_{HCl}} = 18[/math]

 

is correct

[popcornfrenzy]

13 hours ago, studiot said:

Good morning.

What subject are you studying this in, and at what level ? Is it General Science or something at higher level ?

Muriatic acid is a very old name - in all the 60 years since I have known anything about it I have never seen the name used.

So I will try to address other older conventions in my reply as well.

I'm currently in my third year as an environmental science student, this is for my subject in Analytical Chemistry. Actually for industrial, and domestic uses, the name muriatic acid is still used in my country, Philippines.

13 hours ago, studiot said:

So you should look carefully at the labels for one of the above abbreviations on the labels you are told to read.

Without this information you cannot answer the question.

We were told to check the labels on the internet in search for common concentrations of these chemicals.

 

13 hours ago, studiot said:

Either way the % is a fraction of the total amount  - which is the sum of the water and the HCl in a given mass or volume

Does this mean that regardless if its w/w or v/v; the equation you mentioned is still applicable? 

 

Thanks for the reply

[studiot]

8 hours ago, popcornfrenzy said:

I'm currently in my third year as an environmental science student, this is for my subject in Analytical Chemistry. Actually for industrial, and domestic uses, the name muriatic acid is still used in my country, Philippines.

Thanks that useful.  I can expand the explanation in the light of this. Also I added the comment about the old name as it is an example of old use that people still come across in life or literature. For example many still use weight (eg the pharmaceutical industry) not mass, as of course they weigh things to get the mass. They still use W, not M is mass ratios. Also M can be used for the mole ratio, which is also fundamental.

8 hours ago, popcornfrenzy said:

We were told to check the labels on the internet in search for common concentrations of these chemicals.

There you are then.

How much do you know or need to know about concentrations and dilutions ?

 

8 hours ago, popcornfrenzy said:

Does this mean that regardless if its w/w or v/v; the equation you mentioned is still applicable? 

Yes, although I didn't change the volume formula to suit.

So long as you use the same units for all the quantities it doesn't matter.

But there is an added twist with volumes as you may need the densities to make the calculations work properly.

The mass ratio is the fundamental fraction.

You may have noticed that it is easier to use the fact that sum of the % masses of the two substances in the mixture must add to 100% than to use my fraction.

It is not necessarily the case that when you add two liquids together the resultant volume is the sum of the individual volumes, the volumes must be corrected to the mass ratio  (using the densities) as this is the always true for masses or fore mole counts.

In fact at normal temperatures HCl is a gas so will dissolve without much volume increase and you may have pressure as a measure and need to use the gas laws to get to the mass or mole ratio.

[MartaSher]

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