GCSE Chemistry - Acids and Bases #34

Summary

This video explores the pH scale, which measures a solution's acidity or alkalinity from 0 to 14. It explains that a pH of 7 is neutral, while lower values are acidic and higher values are alkaline. Examples include stomach acid at pH 2 and bleach at pH 12. Measuring pH can be done with indicators or a pH probe for more precision. Acids are defined as substances with a pH less than 7, releasing hydrogen ions, while bases and alkalis (a subgroup of bases that are water-soluble) have a pH greater than 7, forming hydroxide ions. The video also covers neutralization reactions between acids and bases, resulting in salts and water, and highlights common acids and bases like hydrochloric acid and sodium hydroxide.

Takeaways

• 🔍 The pH scale is a measure of how acidic or alkaline a solution is, ranging from 0 to 14.
• 🍋 Low pH numbers indicate high acidity, with stomach acid being around pH 2.
• 🌧️ Acid rain has a pH of about 4, showing its acidic nature.
• 🧼 Alkaline substances like washing up liquid have a pH around 9, while bleach is around 12.
• 💧 Pure water is neutral with a pH of 7, neither acidic nor alkaline.
• 🌈 pH can be measured using indicators, which are chemical dyes that change color based on pH levels.
• 🔬 A more precise method to measure pH is by using a pH probe connected to a meter, providing a numerical reading.
• 🧪 Acids are substances that form aqueous solutions with a pH less than 7, releasing hydrogen ions.
• 🧴 Alkalis are a subgroup of bases that are soluble in water and form solutions with a pH greater than 7, releasing hydroxide ions.
• ⚖️ A neutralization reaction occurs when an acid and a base react, producing a salt and water, with a neutral pH of 7.
• 📚 Common acids include hydrochloric, sulfuric, and nitric acids, while common bases are often hydroxides or carbonates like sodium hydroxide or calcium carbonate.

Q & A

What is the pH scale and what does it measure?

The pH scale is a measure of how acidic or alkaline a solution is, ranging from 0 to 14. Low numbers indicate acidity, high numbers indicate alkalinity, and a pH of 7 is neutral, like pure water.

What is the pH level of stomach acid and acid rain?

The pH level of stomach acid is around 2, which is highly acidic, and acid rain has a pH of about 4.

What is the pH of washing up liquid and bleach?

Washing up liquid has a pH of around 9, and bleach has a pH of around 12, indicating they are alkaline.

How can pH be measured?

pH can be measured using indicators, which are chemical dyes that change color depending on the pH, or by using a pH probe connected to a pH meter for more accurate electronic measurements.

What is the difference between a wide range indicator and a pH probe?

A wide range indicator is a type of pH indicator that changes color across a wide range of pH values, while a pH probe provides a numerical reading and is more accurate and precise.

What is an acid and how is it defined in terms of pH?

An acid is defined as any substance that forms aqueous solutions with a pH of less than seven, due to the release of hydrogen ions in water.

What are bases and alkalis, and how do they differ in terms of pH?

Bases are substances with a pH greater than seven, while alkalis are a subgroup of bases that are soluble in water and form solutions with a pH greater than seven.

What happens when an acid and a base react together?

When an acid and a base react, a neutralization reaction occurs, producing a salt and water. The pH of the products should be seven because they are neutral.

What are some common acids and bases mentioned in the script?

Common acids include hydrochloric acid, sulfuric acid, and nitric acid, while common bases are generally hydroxides or carbonates like sodium hydroxide or calcium carbonate.

Why is it important to know the pH of substances?

Knowing the pH of substances is important for understanding their chemical properties, such as their reactivity and potential effects on the environment or biological systems.

How do hydrogen ions and hydroxide ions play a role in neutralization reactions?

In neutralization reactions, hydrogen ions (H+) from the acid and hydroxide ions (OH-) from the base combine to form water (H2O), resulting in a neutral pH of seven.

Outlines

00:00

🔍 Understanding the pH Scale

This paragraph introduces the pH scale, which is a measure of how acidic or alkaline a solution is. It ranges from 0 to 14, with 0 being highly acidic, 14 highly alkaline, and 7 being neutral, like pure water. Examples are given to illustrate the pH levels of various substances, such as stomach acid (around pH 2) and bleach (around pH 12). Two methods of measuring pH are discussed: using indicators, which are chemical dyes that change color based on pH, and using a pH probe connected to a meter for more accurate and precise electronic measurements.

Keywords

💡pH scale

The pH scale is a logarithmic scale used to specify the acidity or alkalinity of a solution. It ranges from 0 to 14, with 7 being neutral. In the video, the pH scale is central to understanding the concept of acidity and alkalinity, with examples given such as stomach acid at around pH 2 and bleach at around pH 12.

💡acids

Acids are substances that form aqueous solutions with a pH of less than seven. They release hydrogen ions (H+) when dissolved in water, which is what makes the solution acidic. The video mentions common examples like hydrochloric acid and sulfuric acid.

💡alkalis

Alkalis are a subgroup of bases that are soluble in water and form solutions with a pH greater than seven. They produce hydroxide ions (OH-) in water. The video uses washing up liquid as an example of an alkali with a pH of around nine.

💡indicators

Indicators are chemical dyes that change color depending on the pH of a solution. They are used to measure pH visually. The video explains that universal indicator is a common type that changes color across a wide range of pH values.

💡pH probe

A pH probe is an electronic device used to measure the pH of a solution. It is dipped into the solution, and the pH is displayed on a meter. The video highlights the accuracy and precision of pH probes over indicators, as they eliminate the need for human interpretation of color changes.

💡neutralization reaction

A neutralization reaction occurs when an acid and a base react to form a salt and water. This reaction always results in a solution with a pH of seven, which is neutral. The video explains this concept using the reaction between hydrochloric acid and sodium hydroxide as an example.

💡hydrogen ions

Hydrogen ions (H+) are released by acids when they are dissolved in water. These ions are responsible for the acidic nature of the solution. The video discusses how the presence of hydrogen ions defines an acidic solution on the pH scale.

💡hydroxide ions

Hydroxide ions (OH-) are formed when alkalis dissolve in water. These ions contribute to the alkaline nature of the solution. The video mentions that alkalis, such as sodium hydroxide, form hydroxide ions in water.

💡bases

Bases are substances that form aqueous solutions with a pH greater than seven. They are the opposite of acids and typically accept hydrogen ions. The video defines bases and distinguishes them from alkalis, noting that alkalis are a type of base that is soluble in water.

💡salts

Salts are the products formed when an acid and a base undergo a neutralization reaction. The video explains that the reaction between hydrochloric acid and sodium hydroxide results in the formation of sodium chloride, which is a salt.

💡universal indicator

Universal indicator is a wide-range pH indicator that changes color across the entire pH scale. It is used to visually determine the pH of a solution, with the video providing a color chart from deep red (low pH) to bluey purple (high pH).

Highlights

The pH scale measures how acidic or alkaline a solution is, ranging from 0 to 14.

Low pH numbers indicate high acidity, while high numbers indicate high alkalinity.

A pH of 7 is neutral, like pure water, which is neither acidic nor alkaline.

Stomach acid has a pH of around 2, aiding in bacteria digestion.

Acid rain has a pH of approximately 4, indicating its acidic nature.

Washing up liquid has a pH of around 9, classifying it as an alkali.

Bleach used for cleaning bathrooms has a pH of about 12, making it highly alkaline.

Indicators are chemical dyes that change color based on pH levels.

Universal indicator provides a color range from red to bluey purple across the pH scale.

pH probes connected to meters offer a more accurate and precise pH measurement method.

Acids are substances that form aqueous solutions with a pH less than seven.

Bases are substances with a pH greater than seven, while alkalis are a subgroup of soluble bases.

Alkalis form hydroxide ions (OH-) in water, contributing to their alkaline nature.

Neutralization reactions between acids and bases produce salts and water.

The pH of neutralization reaction products is typically seven, indicating neutrality.

Common acids include hydrochloric, sulfuric, and nitric acid, while bases often include hydroxides or carbonates.

Learning the properties of common acids and bases is beneficial for understanding their applications.

Transcripts

in today's video we're going to look at

the ph scale and see what acids and

alkalis are

ph is really just a measure of how

acidic or alkaline a solution is

and it's measured on a scale from 0 to

14

with low numbers being most acidic and

high numbers being most alkaline

and if the substance is neutral like

pure water then the ph would be seven

which is neither acidic nor alkaline

to give you some idea of what all of

this means the acid in your stomach

which helps you to cure bacteria has a

ph of around two

while acid rain is around ph4

then for alkalis washing up liquid has a

ph of around nine and the bleach we use

to clean bathrooms has a ph of around

12.

be aware though you don't have to

remember these specific examples there

just to give you some context

now we can measure ph in a couple of

different ways

one is to use some kind of indicator

which are a group of chemical dyes that

change color depending on the ph

and different indicators will change

color at different phs

some indicators contain a mixture of

these different dyes though so their

color will slowly change across a wide

range of ph's

so we often refer to them as wide range

indicators

the most common example is universal

indicator

which gives the colors we've shown our

ph scale here ranging from deep red at a

very low and acidic ph to yellow green

and then bluey purple as we increase the

ph and it becomes more alkaline

the other way to measure ph is to use a

ph probe connected to a ph meter

by dipping the probe into a solution we

can electronically measure the ph and

get a numerical reading on the meter

the benefit of the probe compared to an

indicator is that it can be much more

accurate and precise because it doesn't

involve humans guessing shades or

particular colors

and as a general rule measurements that

remove the need for human judgment are

going to be more reliable

the next thing we need to look at is

what exactly makes something an acid

you can define an acid as any substance

that forms aqueous solutions with a ph

of less than seven

and the reason for this is that acids

release hydrogen ions in water

which make the solution acidic

on the other side of the scale we have

bases which we define as any substance

with a ph greater than seven

meanwhile alkalis which we mentioned

before are actually a subgroup of bases

that are soluble in water

so we would say that an alkali is a base

that dissolves in water to form a

solution with a ph greater than seven

and these alkalis form o h minus ions in

water which we call hydroxide ions

if we react an acid and a base together

then we get a neutralization reaction

which will always produce a salt and

water

for example hydrochloric acid plus

sodium hydroxide which are the most

common acid and base

will react to form sodium chloride which

is a salt plus water

another way to show these neutralization

reactions is in terms of hydrogen ions

and hydroxide ions

where h plus from the acid and o h minus

from the base combine to form h2o

and because the acid and base have both

been neutralized in these sorts of

reactions the ph of the products should

be seven because they're neutral

before we finish i just want to point

out some of the common acids and bases

that you'll come across in the course

the main acids are hydrochloric acid

sulfuric acid and nitric acid

while the common bases are generally

hydroxides or carbonates like sodium

hydroxide or calcium carbonate

there are loads more but it's definitely

worth learning these few as they crop up

a lot

anyway that's all for today so hope you

enjoyed this video and we'll see you

next time