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General information:

Laboratory practice:

What common materials are acids and bases?

Due date:

Feedback date:

One week after delivering the activity

Modality:

Individual

Delivery mode:

In the classroom and blackboard platform

Percentage:

100

Didactic information:

- Purpose:

- Know the pH of different common substances.

- Learn to use a pH sensor.

- Register and process the obtained data through tables and graphs.

- Resources:

- Complementary bibliography.

- Graph paper.

- TI-nspire CX calculator

- Instructions:

- In the beginning of the class, the profesor witll explain the generalities about acids and bases (common substances, pH scale and measuring instruments).

- Afterwards, the profesor will give instructions about the demonstrative laboratory practice methodology and will perform the experimentation.

- Individually, the student will answer a classwork given by the professor with the obtained observations.

- At the end, the results obtained from the demonstrative laboratory practice will be shared with the class.

- Evaluation criteria:

- Checklist (Attached).

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UNIVERSIDAD DE MONTERREY[pic 9]

DIVISIÓN DE EDUCACIÓN MEDIA SUPERIOR

ACADEMIA DE CIENCIAS NATURALES

AUTUMN 2015

ENVIRONMENTAL SYSTEMS

Name: ___________________________________________________ ID: __________________

Date: __________________________ Room: _______________

Demonstrative Laboratory Practice: Types of chemical reactions: What common substances are acids and bases?

Purpose:

To know the pH of different common substances. Learn to use a pH sensor. Register and process the obtained data through tables and graphs.

Experimentation skills:

Observation: To become aware through the senses of a change, or transformation in an object or variable during testing of a fact or phenomenon then registering it.

Variable identification: Clearly identify the: dependent (measured), independent (manipulated) and controlled variables (constants) that are pertinent and are part of the experiment, which directly affects the results.

Manipulation: Operate an object with hands or any instrument.

Data Register: To take notes through: tables, lists or any other way the qualitative or quantitative data obtained by measurement or experimentation, including units or uncertainties.

Introduction:

In our daily life we use different substances, some of them as home cleaning products, others as food. In this practice the investigation question is: Are common home substances acid or bases? Besides answering this question, we will determine if rainwater is influenced by pollution, converting it into acid rain.

We will start by learning that the acidity or basicity of substances may be determined by the pH measurement. A scale is used to measure the pH of substances, which is the way to express the hydrogen ion concentration in solutions. The scale has a range of 1 to 14. In the present days, there are pH measuring devices, which are easy to use and reliable generally. Although in the methodology of this practice the use of an electronic pH measuring device is described, there is another way to determine this parameter that is simpler but less accurate; this method consists on using litmus paper strips. This strips impregnate with the substance to be analyzed and change their color depending on whether the substance is acid or basic.

Its important to aknowledge the pH of the common home substances, to define if we manipulate acid substances (pH between 1.0 and 6.9), neutral (pH 7.0) or basic (pH between 7.1 and 14.0) in our daily lives.

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Theoretical framework:

According to Buthelezi (2008), all the water solutions contain hydrogen ions (H +) and hydroxide ions (OH-). The relative amounts of both ions determine if an aqueous solution is acid, basic or neutral. Arrhenius’ model states that an acid is a substance that contains hydrogen and ionizes to produce hydrogen ions in an aqueous solution and a base is a substance that contains a hydroxide group and dissociates to produce a hydrogen ion in an aqueous solution.

“The concentration of this ions is measured with the pH scale proposed by S. Sorensen in 1909, that determine that acid solutions have pH values lower than 7, basic solutions have a pH greater than 7, therefore considering the pH values of 7 as neutral” (Buthelezi, 2008).

“The pH of a liquid or solution is an important piece of information in science often. The measurement of pH may be done simply and quickly using a pH strip or a pH sensor. The pH paper contains indicators (chemical substances that change in color according to the acid or basic form of a solution). The pH sensors are electronic devices that are used to measure pH, they are composed of a probe that is submerged in a solution, and a digital reading. PH meters are much more accurate than pH strips” (Krahe, 2005).

Hypothesis: