The Impacts of Hydrochloric Acid Concentration on the solubility of Salt and
Sugar - Sandy Tran
Literature Review:
Despite having various experiments on the effects of temperature and pressure on
solubility, there has not been much discussion on the impacts of hydrochloric acid
concentration. To its core, the concentration of hydrochloric acid directly links to the pH
scale as diluting an acid will increase towards a pH of 7 where the concentration of H+
ions decreases(BBC Bitesize, 2021). Linking to this, factors that might affect salt
solubility in progressively more concentrated solvents is the common ion effect. The
common ion effect is when an ionic solution comes into contact with another ionic
compound containing a common ion. Due to these conditions, the ionic substance's
solubility is greatly reduced as reinforced by Le Chatelier's principle. Where Le
Chatelier’s Principle states that “If a dynamic equilibrium is disturbed by changing the
condition, the position of equilibrium moves to counteract the change” (Admin, 2015).A
range of factors can shift this equilibrium including pressure, temperature, pH and the
number of products and reactants.
These molecules, compounds and lattice are structured from their physical properties
and interactions of atoms. The 2 targeted types of chemical bondings made in between
atoms are ionic and covalent. Ionic compounds are formed between a metal and
non-metal and arranged in an ionic lattice. Ionic bonds rely on the transfer of electrons in
valence shells, ultimately creating strong electrostatic forces of attraction between
oppositely charged ions.
Covalent molecular structures are bonded individually with covalent intramolecular
bonds where neighbouring molecules experience weak intermolecular forces. Strong
covalent bonds are formed through the sharing of valence electrons.
Despite being strongly bonded together within molecules, the bonds between these
molecules are much weaker and are easier to break. Covalent compounds are not
limited to molecular structuring; they can form covalent networks. Examples of covalent
network lattice structures include diamond, structured as rigid tetrahedral crystals. In
between each carbon atom are strong intramolecular forces similar to that of ionic
lattices. The characteristics seen within these compounds explains their respective
melting and boiling points due to the amount of energy required to break these
intramolecular and molecular bonds.
(Helmenstine, 2020)
Since intramolecular bonds require much more
energy to break, structures like ionic and covalent
network lattices have a higher melting and boiling
point relative to covalent molecular compounds.
The structure of these covalent molecules can be
predicted by the VSEPR theory where it
describes how electron pairs are arranged in
such a way to maximise the bond strength and
minimize interactions between the bonds and
unshared pairs of electrons. To put this into perspective, since water
has two lone pairs of electrons on the same side of the molecule they
repel each other as they are only attracted to the oxygen atom. This
repulsion causes the bonds of hydrogen with oxygen to be pushed to
one side, creating a bent shape. (Purdue.edu, 2021)
Furthermore, salt will dissociate into its
respective ions whereby sugar breaks up
physically into individual molecules. This
concept correlates with electronegativity, the
measure of an atom’s ability to attract
electrons towards itself when forming bonds.
Ionic and covalent compounds respond
differently to each other as ionic bonds form
when two elements have a large difference in
electronegative activity (ΔEN>1.7), whereas covalent bonds have a smaller difference.
Since each atom has a similar pull on electrons, the electrons are shared. In general,
metals give a low electronegativity where non-metals respond contrarily. Moving across
a period showcases a decrease in atomic radii indicating that valence electrons
experience a greater nuclear charge. As atoms are more likely to gain electrons,
electronegativity increases. Moving down a group rejects this trend by decreasing as
atomic radii get larger in each successive shell. Polarity and electronegativity have a
directly proportional relationship as electrons shift towards greater electronegative atoms
in intramolecular bonds. Polarity, referring to the distribution of the electrical charge over
the bonded atoms in molecules and compounds. (Chemistry LibreTexts, 2018) The
greater the disparity in electronegativity, the more polarised the electron distribution and
the greater the atoms' partial charges. With the exception of noble gases, strong ionic
bonds form from the LHS and RHS
observed between metal and
non-metal. Covalent bonds however
rely on the interaction of non-metals
located on just the RHS of the
periodic table. Both these
intramolecular forces are much
stronger relative to intermolecular
forces of dipole-dipole, dispersion,
ion-dipole and hydrogen bonds.
(Helmenstine, 2019)
Research question: Does the
concentration of hydrochloric acid
impact the solubility of salt and sugar?
Aim
To investigate the effects of varying concentration of hydrochloric acid on the solubility of
salt and sugar.
Hypothesis
If the concentration of hydrochloric acid is high, then the solutes, salt and sugar, will
have a decreased saturation point because there are more ions to reinforce the common
ion effect.
Equipment
- Electronic scale
- Magnetic Stirrer
- Beaker
- 2 molar HCl acid
- 8 50mL measuring cylinder
- 1kg Sugar
- 1kg salt
- Teaspoon
Method
Part I
1. Rinse all apparatus with tap water
2. Pour 0mL of water into 50 mL measuring cylinder
3. Pour HCl acid until solution reacher 40mL graduated marker
4. Put filled measuring cylinder aside for method part II
5. Repeat steps 2-3 increasing the amount of water by increments 4mL until 40mL
of water.
Part II
1. Rinse all apparatus with tap water
2. Set up all apparatus
3. Add about 20g of salt to the beaker. It does not have to be exactly 30 g and
record the mass of the beaker and the salt to the nearest hundredth of a gram.
4. Transfer a selected acid solution into a beaker
5. Place beaker onto electric stirrer and add magnetic piece into the centre of the
beaker
6. Turn control knob and adjust speed to maximum, making sure to be careful of
spills.
7. Add a table spoon of salt to the beaker.
8. Stir solution for 2 minutes
9. Repeat steps 7-8 until no more salt will dissolve after being stirred.
10. Weigh the beaker with the remaining salt and record.
11. Repeat steps 2-8 using each respective solution of different concentrations of HCl
acid.
Risk Assessment
Risk
Precaution
Sliced skin from broken
glass
Injury from skin/eye
contact with acid
Treatment
Be careful handling
glassware and notify
supervisor if their is broken
glass present
-
Handle solutions with
special caution and wear
goggles
-
-
Clot affected area to
prevent blood loss
Use first aid
Immediately flush
area with abundant
water for at least 10
minutes
Variables
Variables
Independent
-
Concentrations of
HCl acid (M)
Type of solute
Variables to be
controlled
Dependent
-
Solubility of solute
(g/mL)
-
Temperatures
Environment
Branding of sugar
and salt
Molarity of HCl acid
Results
Solubility of Solutes
Salt
Sugar (sucrose)
Concentr
ation of Trial 1
HCl (M)
(g/100
ml)
Trial
2
Trial 3 Avg
Avg
Trial 1 Trial 2 Trial 3 Avg
(g/10 (g/100 (g/100 (molL (g/100 (g/100 (g/100 (g/10 Avg
0ml) ml)
ml)
)
ml)
ml)
ml)
0ml) (molL-)
0
33.85
32.13 33.53
33.17 5.68
60.78 62.38 67.58 63.58 1.86
0.25
31.08
30.98 32.35
31.47 5.39
57.43 57.53 60.23 58.40 1.71
0.5
33.03
29.85 31.21
31.36 5.37
47.53 53.42 48.83 49.93 1.46
0.75
28.12
25.83 28.71
27.55 4.71
44.43 45.05 46.13 45.20 1.32
1
26.25
24.83 26.29
25.79 4.41
43.48 46.73 42.53 44.25 1.29
1.25
25.58
23.35 24.32
24.42 4.18
40.92 46.24 40.13 42.43 1.24
1.5
23.31
22.28 23.28
22.96 3.93
38.81 43.23 43.55 41.86 1.22
1.75
22.23
21.55 22.13
21.97 3.76
41.32 43.08 40.05 41.48 1.21
2
20.28
21.38 21.28
20.98 3.59
38.43 40.53 40.33 39.76 1.16
Discussion
Relevant research within the literature review had aligned and provided a rough
understanding of the perceived outcomes. The average solubility of sugar reaching its
saturation point had declined from 63.58g/100mL in tap water to a decreased amount of
39.76g/100mL in 2M hydrochloric acid. Similarly, the same trend occurred with salt as its
average solubility was initially 33.17g/100mL, steadily declining to 20.98g/100mL. A
common trend where the solubility of both solutes decreased at a uniform and constant
rate. In terms of molarity, salt was able to dissolve more than sucrose despite having
more mass. The molarity of sucrose from 0M-2M HCl acid had ranged from
1.86-1.16Mol/L where salt had a range of 5.68-3.59Mol/L respectively.
As discussed in the literature review, the explanation behind why salt solubility in a more
concentrated HCl solution had decreased was due to the common ion effect. The
dissociation of HCl had made pre-existing ion-dipoles with the polar molecules and since
salt will dissociate into sodium and chloride ions, chloride ions were common. Adding a
common ion into the solution will cause a shift in the equilibrium of NaCl. With an
increase in chlorine ions, the application of Le Chatelier’s principle will shift the
equilibrium towards the reactants of NaCl(Khan Academy 2014). This limits the
dissociation of salt in more concentrated solutions implicating the decreasing trend in
solubility. Sugar is a covalent molecule and unlike the ionic compound of salt, will
dissolve molecule by molecule. Increasing the concentration of HCl acid forms more
hydrogen and chlorine ions leading to fewer bonds that can form with sucrose. Despite
sugars' high weight per volume ratio to salt, the resulting molarity was nowhere near
salt. A molecule of sucrose weights much more than salt with a molar weight of
342.3g/mol as opposed to salt where it is 58.44g/mol. Since a single sucrose molecule
can make multiple hydrogen bonds with water, it uses up all possible formations of
hydrogen bonds faster than it would with sodium chloride ions. Since these ions are
single atoms, each ion can create strong ion dipoles with polar water molecules until all
bonds have been made.
The fundamentals of the experiment, accuracy, reliability and validity were challenged
throughout the procedure. The experiment overall had a highly rated validity as the
method had satisfied the aim and fulfilled the hypothesis. All variables were well
maintained and appropriate towards the aim and purpose of the experiment. Its accuracy
was moderate as there was difficulty achieving an exact number of solute dissolved in a
solvent, a random error. The undissolved solute in the solvent was not compensated for,
creating impacts seen throughout all results. However, the electronic scale used
measured up to a hundredth of a gram, heightening its accuracy. Reliability can be
concluded as high due to their similarities in results. Despite having a slight inaccuracy
of solubility as listed above, all results had very similar outcomes thus being offered high
reliability. Furthermore, the experiment was repeated a total of 3 trials across each level
of concentration per solute.
During the process of the experiment, there were various limitations regarding the
accuracy of the data. Since the measurements did not consider the leftover remnants, it
caused the inability to calculate the exact amount of dissolved solute. Avoiding this
dilemma requires implementing filtration and evaporation of the solution to get an exact
number of dissolved solute. Limitations were reinforced by not monitoring external
constituents of pressure, temperature and the foreign substances in the tap water. These
limitations were due to the lack of time and accessibility as the data collected were over
multiple sessions where the weather had varied. Strategies to reduce the impacts
include performing the experiment in one procedure and using deionized water.
To achieve a better insight into this experiment, different variables of both the solvent
and solute should be used. Where altering the acid will give the idea of how acids
respond to the solubility of salt and sugar, modifying the solute will give a better
understanding of the solubility trends dependent on HCl acid concentration.
Conclusion
Overall, the experiment conclusively answers the aim of the effects of HCl acid
concentration on the solubility of salt and sugar. The hypothesis had stated that the more
concentrated the solvent was, the lower the saturation point in both cases, and as
supported by the report it was correct. A common trend has been seen in both cases
where the more concentrated the solvent is with HCl acid, the less soluble it is due to the
common ion effect and the limitations of formation of all possible bonds.
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