The science of nutrition and healthy eating
The science of nutrition and healthy eating

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

The science of nutrition and healthy eating

2.1 The pH scale

The unfortunate accident to Alexis St Martin led doctors to understand more about the workings of the stomach than ever before. Let’s start by looking in more detail at the acid.

A special scale is used to measure how acidic a solution is – the pH scale (Figure 3). Anything reading less than 7 on the pH scale is an acid. The more acidic it is, the lower the number. Water, which is neutral, has a pH value of 7. Anything greater than 7 is said to be alkaline. The pH of stomach acid is about 2, less acidic than car battery acid (pH 1) but more acidic than lemon juice (pH 2.4) and vinegar (pH 2.9). Bicarbonate of soda is alkaline – a solution of it has a pH of about 8.

An image of indicator paper testing pH scale.
Figure 3 Indicator paper detects pH by changing colour – the colours and numbers on the right show the pH value

Some people get indigestion or ‘heartburn’. This can be caused by the acid from the stomach irritating the lower part of the oesophagus, which is called acid reflux. If the condition occurs only occasionally and is mild, the symptoms can be alleviated by taking over-the-counter medicines called antacids. These contain alkaline substances which neutralise the stomach acid, usually producing carbon dioxide gas at the same time, which may cause wind (flatulence).


Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371