give preparation and uses of plaster of paris?
Answers
Answer:
Plaster of paris, quick-setting gypsum plaster consisting of a fine white powder (calcium sulfate hemihydrate), which hardens when moistened and allowed to dry. Known since ancient times, plaster of paris is so called because of its preparation from the abundant gypsum found near Paris.
Explanation:
Answer:
Plaster of paris, quick-setting gypsum plaster consisting of a fine white powder (calcium sulfate hemihydrate), which hardens when moistened and allowed to dry. Known since ancient times, plaster of paris is so called because of its preparation from the abundant gypsum found near Paris.
Explanation:
What is Plaster of Paris?
Plaster of Paris is a popular substance that is utilized most commonly for sculpting materials and in gauze bandages. While we have seen many applications of this material in our everyday lives if we try to understand its chemistry, plaster of Paris is a white powdery chemical compound which is hydrated calcium sulfate that is usually obtained from calcining gypsum.
Plaster of Paris is also referred to as Gypsum plaster. The chemical formula of plaster of Paris is written as CaSO4·H2O or 2CaSO4·H2O.
Preparation of Plaster of Paris
Plaster of Paris is manufactured by heating gypsum at 423K or 150o C/300o F.
CaSO4·2H2O + heat → CaSO4·0.5H2O + 1.5H2O (discharged as steam)
On heating gypsum at 423 K, it loses water molecules and becomes calcium sulfate hemihydrate. This product is known as the plaster of Paris. However, when water is mixed with dry plaster of Paris, it re-structures into gypsum. As for the process of hardening and setting, it starts around 10 minutes subsequent to blending and is completed in about 45 minutes. It is not completely set for 70-75 hours.
Also Read: Calcination
On the other hand, when plaster or gypsum is heated at temperatures higher than 266 °F (130 °C), then we obtain hemihydrate. Other compounds are also formed when gypsum is formed at different temperatures. For example;
When it is heated to about 180 °C, γ-anhydrite is formed. Similarly, when it is heated above 250 °C, β-anhydrite or dead burned plaster is formed and ita completely anhydrous product.
Characteristics of Gypsum Plaster
Plaster of Paris is usually a white dry plaster powder. It can be effectively worked with metal apparatuses or even abrasive sheets and can be shaped as per the requirements. The strength of plaster of Paris is not as strong as other compounds and it often requires external support when a large amount is used. It is often applied in the form of a quick-setting paste with water